diff --git a/skimage/io/__init__.py b/skimage/io/__init__.py
index 5e701a51..316253ca 100644
--- a/skimage/io/__init__.py
+++ b/skimage/io/__init__.py
@@ -1,49 +1,34 @@
-__doc__ = """Utilities to read and write images in various formats.
+"""Utilities to read and write images in various formats.
 
 The following plug-ins are available:
 
 """
 
-from ._plugins import use as use_plugin
-from ._plugins import available as plugins
-from ._plugins import info as plugin_info
-from ._plugins import configuration as plugin_order
-from ._plugins import reset_plugins as _reset_plugins
-
+from .manage_plugins import *
 from .sift import *
 from .collection import *
 
 from ._io import *
+from ._image_stack import *
 from .video import *
 
 
-available_plugins = plugins()
+reset_plugins()
+
+WRAP_LEN = 73
 
 
-def _load_preferred_plugins():
-    # Load preferred plugin for each io function.
-    io_funcs = ['imsave', 'imshow', 'imread_collection', 'imread']
-    preferred_plugins = ['matplotlib', 'pil', 'qt', 'freeimage', 'null']
-    for func in io_funcs:
-        for plugin in preferred_plugins:
-            if plugin not in available_plugins:
-                continue
-            try:
-                use_plugin(plugin, kind=func)
-                break
-            except (ImportError, RuntimeError, OSError):
-                pass
+def _separator(char, lengths):
+    return [char * separator_length for separator_length in lengths]
 
-    # Use PIL as the default imread plugin, since matplotlib (1.2.x)
-    # is buggy (flips PNGs around, returns bytes as floats, etc.)
-    try:
-        use_plugin('pil', 'imread')
-    except ImportError:
-        pass
 
-def reset_plugins():
-    _reset_plugins()
-    _load_preferred_plugins()
+def _format_plugin_info_table(info_table, column_lengths):
+    """Add separators and column titles to plugin info table."""
+    info_table.insert(0, _separator('=', column_lengths))
+    info_table.insert(1, ('Plugin', 'Description'))
+    info_table.insert(2, _separator('-', column_lengths))
+    info_table.append(_separator('-', column_lengths))
+
 
 def _update_doc(doc):
     """Add a list of plugins to the module docstring, formatted as
@@ -52,27 +37,24 @@ def _update_doc(doc):
     """
     from textwrap import wrap
 
-    info = [(p, plugin_info(p)) for p in plugins() if not p == 'test']
-    col_1_len = max([len(n) for (n, _) in info])
 
-    wrap_len = 73
-    col_2_len = wrap_len - 1 - col_1_len
+    info_table = [(p, plugin_info(p).get('description', 'no description'))
+                  for p in available_plugins if not p == 'test']
 
-    # Insert table header
-    info.insert(0, ('=' * col_1_len, {'description': '=' * col_2_len}))
-    info.insert(1, ('Plugin', {'description': 'Description'}))
-    info.insert(2, ('-' * col_1_len, {'description': '-' * col_2_len}))
-    info.append(('=' * col_1_len, {'description': '=' * col_2_len}))
+    name_length = max([len(n) for (n, _) in info_table])
+    description_length = WRAP_LEN - 1 - name_length
+    column_lengths = [name_length, description_length]
+    _format_plugin_info_table(info_table, column_lengths)
 
-    for (name, meta_data) in info:
-        wrapped_descr = wrap(meta_data.get('description', ''),
-                             col_2_len)
-        doc += "%s %s\n" % (name.ljust(col_1_len),
-                            '\n'.join(wrapped_descr))
+    for (name, plugin_description) in info_table:
+        description_lines = wrap(plugin_description, description_length)
+        name_column = [name]
+        name_column.extend(['' for _ in range(len(description_lines) - 1)])
+        for name, description in zip(name_column, description_lines):
+            doc += "%s %s\n" % (name.ljust(name_length), description)
     doc = doc.strip()
 
     return doc
 
-__doc__ = _update_doc(__doc__)
 
-reset_plugins()
+__doc__ = _update_doc(__doc__)
diff --git a/skimage/io/_image_stack.py b/skimage/io/_image_stack.py
new file mode 100644
index 00000000..ca9896d5
--- /dev/null
+++ b/skimage/io/_image_stack.py
@@ -0,0 +1,35 @@
+import numpy as np
+
+
+__all__ = ['image_stack', 'push', 'pop']
+
+
+# Shared image queue
+image_stack = []
+
+
+def push(img):
+    """Push an image onto the shared image stack.
+
+    Parameters
+    ----------
+    img : ndarray
+        Image to push.
+
+    """
+    if not isinstance(img, np.ndarray):
+        raise ValueError("Can only push ndarrays to the image stack.")
+
+    image_stack.append(img)
+
+
+def pop():
+    """Pop an image from the shared image stack.
+
+    Returns
+    -------
+    img : ndarray
+        Image popped from the stack.
+
+    """
+    return image_stack.pop()
diff --git a/skimage/io/_io.py b/skimage/io/_io.py
index eb704a6f..97f8718e 100644
--- a/skimage/io/_io.py
+++ b/skimage/io/_io.py
@@ -1,34 +1,14 @@
-__all__ = ['Image', 'imread', 'imread_collection', 'imsave', 'imshow', 'show',
-           'push', 'pop']
-
-try:
-    from urllib.request import urlopen
-except ImportError:
-    from urllib2 import urlopen
-
-import os
-import re
-import tempfile
 from io import BytesIO
 
 import numpy as np
 import six
 
-from skimage.io._plugins import call as call_plugin
+from skimage.io.manage_plugins import call_plugin
 from skimage.color import rgb2grey
+from .util import file_or_url_context
 
 
-
-# Shared image queue
-_image_stack = []
-
-URL_REGEX = re.compile(r'http://|https://|ftp://|file://|file:\\')
-
-
-def is_url(filename):
-    """Return True if string is an http or ftp path."""
-    return (isinstance(filename, six.string_types) and
-            URL_REGEX.match(filename) is not None)
+__all__ = ['Image', 'imread', 'imread_collection', 'imsave', 'imshow', 'show']
 
 
 class Image(np.ndarray):
@@ -77,33 +57,6 @@ class Image(np.ndarray):
         return return_str
 
 
-def push(img):
-    """Push an image onto the shared image stack.
-
-    Parameters
-    ----------
-    img : ndarray
-        Image to push.
-
-    """
-    if not isinstance(img, np.ndarray):
-        raise ValueError("Can only push ndarrays to the image stack.")
-
-    _image_stack.append(img)
-
-
-def pop():
-    """Pop an image from the shared image stack.
-
-    Returns
-    -------
-    img : ndarray
-        Image popped from the stack.
-
-    """
-    return _image_stack.pop()
-
-
 def imread(fname, as_grey=False, plugin=None, flatten=None,
            **plugin_args):
     """Load an image from file.
@@ -140,14 +93,7 @@ def imread(fname, as_grey=False, plugin=None, flatten=None,
     if flatten is not None:
         as_grey = flatten
 
-    if is_url(fname):
-        _, ext = os.path.splitext(fname)
-        with tempfile.NamedTemporaryFile(delete=False, suffix=ext) as f:
-            u = urlopen(fname)
-            f.write(u.read())
-        img = call_plugin('imread', f.name, plugin=plugin, **plugin_args)
-        os.remove(f.name)
-    else:
+    with file_or_url_context(fname) as fname:
         img = call_plugin('imread', fname, plugin=plugin, **plugin_args)
 
     if as_grey and getattr(img, 'ndim', 0) >= 3:
diff --git a/skimage/io/_plugins/__init__.py b/skimage/io/_plugins/__init__.py
index 48aad58e..e69de29b 100644
--- a/skimage/io/_plugins/__init__.py
+++ b/skimage/io/_plugins/__init__.py
@@ -1 +0,0 @@
-from .plugin import *
diff --git a/skimage/io/_plugins/null_plugin.ini b/skimage/io/_plugins/null_plugin.ini
index ddc45f33..9703aab0 100644
--- a/skimage/io/_plugins/null_plugin.ini
+++ b/skimage/io/_plugins/null_plugin.ini
@@ -1,3 +1,3 @@
 [null]
 description = Default plugin that does nothing
-provides = imshow, imread, _app_show
+provides = imshow, imread, imsave, _app_show
diff --git a/skimage/io/_plugins/null_plugin.py b/skimage/io/_plugins/null_plugin.py
index 70bfd5d8..4eb7adf3 100644
--- a/skimage/io/_plugins/null_plugin.py
+++ b/skimage/io/_plugins/null_plugin.py
@@ -1,4 +1,4 @@
-__all__ = ['imshow', 'imread', '_app_show']
+__all__ = ['imshow', 'imread', 'imsave', '_app_show']
 
 import warnings
 
@@ -17,4 +17,9 @@ def imshow(*args, **kwargs):
 def imread(*args, **kwargs):
     warnings.warn(RuntimeWarning(message))
 
+
+def imsave(*args, **kwargs):
+    warnings.warn(RuntimeWarning(message))
+
+
 _app_show = imshow
diff --git a/skimage/io/_plugins/plugin.py b/skimage/io/manage_plugins.py
similarity index 64%
rename from skimage/io/_plugins/plugin.py
rename to skimage/io/manage_plugins.py
index 5e04f320..08bf1703 100644
--- a/skimage/io/_plugins/plugin.py
+++ b/skimage/io/manage_plugins.py
@@ -2,25 +2,37 @@
 
 """
 
-__all__ = ['use', 'available', 'call', 'info', 'configuration', 'reset_plugins']
-
 try:
-    from configparser import ConfigParser
+    from configparser import ConfigParser  # Python 3
 except ImportError:
-    from ConfigParser import ConfigParser
+    from ConfigParser import ConfigParser  # Python 2
 
 import os.path
 from glob import glob
 
 
+__all__ = ['use_plugin', 'call_plugin', 'plugin_info', 'plugin_order',
+           'reset_plugins', 'find_available_plugins', 'available_plugins']
+
+
+# The plugin store will save a list of *loaded* io functions for each io type
+# (e.g. 'imread', 'imsave', etc.). Plugins are loaded as requested.
 plugin_store = None
 
 plugin_provides = {}
 plugin_module_name = {}
 plugin_meta_data = {}
 
+preferred_plugins = {
+    # Default plugins for all types (overridden by specific types below).
+    'all': ['matplotlib', 'pil', 'qt', 'freeimage', 'null'],
+    # Use PIL as the default imread plugin, since matplotlib (1.2.x)
+    # is buggy (flips PNGs around, returns bytes as floats, etc.)
+    'imread': ['pil'],
+}
 
-def reset_plugins():
+
+def _clear_plugins():
     """Clear the plugin state to the default, i.e., where no plugins are loaded
 
     """
@@ -30,8 +42,47 @@ def reset_plugins():
                     'imshow': [],
                     'imread_collection': [],
                     '_app_show': []}
+_clear_plugins()
 
-reset_plugins()
+
+def _load_preferred_plugins():
+    # Load preferred plugin for each io function.
+    io_types = ['imsave', 'imshow', 'imread_collection', 'imread']
+    for p_type in io_types:
+        _set_plugin(p_type, preferred_plugins['all'])
+
+    plugin_types = (p for p in preferred_plugins.keys() if p != 'all')
+    for p_type in plugin_types:
+        _set_plugin(p_type, preferred_plugins[p_type])
+
+
+def _set_plugin(plugin_type, plugin_list):
+    for plugin in plugin_list:
+        if plugin not in available_plugins:
+            continue
+        try:
+            use_plugin(plugin, kind=plugin_type)
+            break
+        except (ImportError, RuntimeError, OSError):
+            pass
+
+
+def reset_plugins():
+    _clear_plugins()
+    _load_preferred_plugins()
+
+
+def _parse_config_file(filename):
+    """Return plugin name and meta-data dict from plugin config file."""
+    parser = ConfigParser()
+    parser.read(filename)
+    name = parser.sections()[0]
+
+    meta_data = {}
+    for opt in parser.options(name):
+        meta_data[opt] = parser.get(name, opt)
+
+    return name, meta_data
 
 
 def _scan_plugins():
@@ -40,19 +91,13 @@ def _scan_plugins():
 
     """
     pd = os.path.dirname(__file__)
-    ini = glob(os.path.join(pd, '*.ini'))
+    config_files = glob(os.path.join(pd, '_plugins', '*.ini'))
 
-    for f in ini:
-        cp = ConfigParser()
-        cp.read(f)
-        name = cp.sections()[0]
-
-        meta_data = {}
-        for opt in cp.options(name):
-            meta_data[opt] = cp.get(name, opt)
+    for filename in config_files:
+        name, meta_data = _parse_config_file(filename)
         plugin_meta_data[name] = meta_data
 
-        provides = [s.strip() for s in cp.get(name, 'provides').split(',')]
+        provides = [s.strip() for s in meta_data['provides'].split(',')]
         valid_provides = [p for p in provides if p in plugin_store]
 
         for p in provides:
@@ -61,12 +106,45 @@ def _scan_plugins():
                       " Ignoring." % (name, p))
 
         plugin_provides[name] = valid_provides
-        plugin_module_name[name] = os.path.basename(f)[:-4]
+        plugin_module_name[name] = os.path.basename(filename)[:-4]
 
 _scan_plugins()
 
 
-def call(kind, *args, **kwargs):
+def find_available_plugins(loaded=False):
+    """List available plugins.
+
+    Parameters
+    ----------
+    loaded : bool
+        If True, show only those plugins currently loaded.  By default,
+        all plugins are shown.
+
+    Returns
+    -------
+    p : dict
+        Dictionary with plugin names as keys and exposed functions as
+        values.
+
+    """
+    active_plugins = set()
+    for plugin_func in plugin_store.values():
+        for plugin, func in plugin_func:
+            active_plugins.add(plugin)
+
+    d = {}
+    for plugin in plugin_provides:
+        if not loaded or plugin in active_plugins:
+            d[plugin] = [f for f in plugin_provides[plugin] \
+                         if not f.startswith('_')]
+
+    return d
+
+
+available_plugins = find_available_plugins()
+
+
+def call_plugin(kind, *args, **kwargs):
     """Find the appropriate plugin of 'kind' and execute it.
 
     Parameters
@@ -85,11 +163,11 @@ def call(kind, *args, **kwargs):
 
     plugin_funcs = plugin_store[kind]
     if len(plugin_funcs) == 0:
-        raise RuntimeError('''No suitable plugin registered for %s.
-
-You may load I/O plugins with the `skimage.io.use_plugin`
-command.  A list of all available plugins can be found using
-`skimage.io.plugins()`.''' % kind)
+        msg = ("No suitable plugin registered for %s.\n\n"
+               "You may load I/O plugins with the `skimage.io.use_plugin` "
+               "command.  A list of all available plugins can be found using "
+               "`skimage.io.plugins()`.")
+        raise RuntimeError(msg % kind)
 
     plugin = kwargs.pop('plugin', None)
     if plugin is None:
@@ -105,7 +183,7 @@ command.  A list of all available plugins can be found using
     return func(*args, **kwargs)
 
 
-def use(name, kind=None):
+def use_plugin(name, kind=None):
     """Set the default plugin for a specified operation.  The plugin
     will be loaded if it hasn't been already.
 
@@ -119,15 +197,19 @@ def use(name, kind=None):
 
     See Also
     --------
-    plugins : List of available plugins
+    available_plugins : List of available plugins
 
     Examples
     --------
 
-    Use the Python Imaging Library to read images:
+    To use Matplotlib as the default image reader, you would write:
 
-    >>> from skimage.io import use_plugin
-    >>> use_plugin('pil', 'imread')
+    >>> from skimage import io
+    >>> io.use_plugin('matplotlib', 'imread')
+
+    To see a list of available plugins run ``io.available_plugins``. Note that
+    this lists plugins that are defined, but the full list may not be usable
+    if your system does not have the required libraries installed.
 
     """
     if kind is None:
@@ -158,36 +240,6 @@ def use(name, kind=None):
         plugin_store[k] = funcs
 
 
-def available(loaded=False):
-    """List available plugins.
-
-    Parameters
-    ----------
-    loaded : bool
-        If True, show only those plugins currently loaded.  By default,
-        all plugins are shown.
-
-    Returns
-    -------
-    p : dict
-        Dictionary with plugin names as keys and exposed functions as
-        values.
-
-    """
-    active_plugins = set()
-    for plugin_func in plugin_store.values():
-        for plugin, func in plugin_func:
-            active_plugins.add(plugin)
-
-    d = {}
-    for plugin in plugin_provides:
-        if not loaded or plugin in active_plugins:
-            d[plugin] = [f for f in plugin_provides[plugin] \
-                         if not f.startswith('_')]
-
-    return d
-
-
 def _load(plugin):
     """Load the given plugin.
 
@@ -201,7 +253,7 @@ def _load(plugin):
     plugins : List of available plugins
 
     """
-    if plugin in available(loaded=True):
+    if plugin in find_available_plugins(loaded=True):
         return
     if not plugin in plugin_module_name:
         raise ValueError("Plugin %s not found." % plugin)
@@ -222,7 +274,7 @@ def _load(plugin):
                 store.append((plugin, func))
 
 
-def info(plugin):
+def plugin_info(plugin):
     """Return plugin meta-data.
 
     Parameters
@@ -242,7 +294,7 @@ def info(plugin):
         raise ValueError('No information on plugin "%s"' % plugin)
 
 
-def configuration():
+def plugin_order():
     """Return the currently preferred plugin order.
 
     Returns
diff --git a/skimage/io/tests/test_collection.py b/skimage/io/tests/test_collection.py
index cf5ef820..1e9fea73 100644
--- a/skimage/io/tests/test_collection.py
+++ b/skimage/io/tests/test_collection.py
@@ -1,88 +1,72 @@
-import sys
 import os.path
 
 import numpy as np
-from numpy.testing import (assert_raises,
-                           assert_equal,
-                           assert_array_almost_equal,
-                           )
-from numpy.testing.decorators import skipif
+from numpy.testing import assert_raises, assert_equal, assert_allclose
 
 from skimage import data_dir
-from skimage.io import ImageCollection, MultiImage
-from skimage.io.collection import alphanumeric_key
-from skimage.io import Image as ioImage
-
-import six
+from skimage.io.collection import ImageCollection, alphanumeric_key
 
 
-try:
-    from PIL import Image
-except ImportError:
-    PIL_available = False
-else:
-    PIL_available = True
+def test_string_split():
+    test_string = 'z23a'
+    test_str_result = ['z', 23, 'a']
+    assert_equal(alphanumeric_key(test_string), test_str_result)
 
 
-class TestAlphanumericKey():
-    def setUp(self):
-        self.test_string = 'z23a'
-        self.test_str_result = ['z', 23, 'a']
-        self.filenames = ['f9.10.png', 'f9.9.png', 'f10.10.png', 'f10.9.png',
-            'e9.png', 'e10.png', 'em.png']
-        self.sorted_filenames = \
-            ['e9.png', 'e10.png', 'em.png', 'f9.9.png', 'f9.10.png',
-            'f10.9.png', 'f10.10.png']
-
-    def test_string_split(self):
-        assert_equal(alphanumeric_key(self.test_string), self.test_str_result)
-
-    def test_string_sort(self):
-        sorted_filenames = sorted(self.filenames, key=alphanumeric_key)
-        assert_equal(sorted_filenames, self.sorted_filenames)
+def test_string_sort():
+    filenames = ['f9.10.png', 'f9.9.png', 'f10.10.png', 'f10.9.png',
+                 'e9.png', 'e10.png', 'em.png']
+    sorted_filenames = ['e9.png', 'e10.png', 'em.png', 'f9.9.png',
+                        'f9.10.png', 'f10.9.png', 'f10.10.png']
+    sorted_filenames = sorted(filenames, key=alphanumeric_key)
+    assert_equal(sorted_filenames, sorted_filenames)
 
 
 class TestImageCollection():
-    pattern = [os.path.join(data_dir, pic) for pic in ['camera.png',
-                                                       'color.png']]
-    pattern_matched = [os.path.join(data_dir, pic) for pic in 
-                                                    ['camera.png', 'moon.png']]
+
+    pattern = [os.path.join(data_dir, pic)
+               for pic in ['camera.png', 'color.png']]
+
+    pattern_matched = [os.path.join(data_dir, pic)
+                       for pic in ['camera.png', 'moon.png']]
 
     def setUp(self):
-        self.collection = ImageCollection(self.pattern)
-        self.collection_matched = ImageCollection(self.pattern_matched)
+        # Generic image collection with images of different shapes.
+        self.images = ImageCollection(self.pattern)
+        # Image collection with images having shapes that match.
+        self.images_matched = ImageCollection(self.pattern_matched)
 
     def test_len(self):
-        assert len(self.collection) == 2
+        assert len(self.images) == 2
 
     def test_getitem(self):
-        num = len(self.collection)
+        num = len(self.images)
         for i in range(-num, num):
-            assert type(self.collection[i]) is np.ndarray
-        assert_array_almost_equal(self.collection[0],
-                                  self.collection[-num])
+            assert type(self.images[i]) is np.ndarray
+        assert_allclose(self.images[0],
+                                  self.images[-num])
 
-        #assert_raises expects a callable, hence this do-very-little func
+        # assert_raises expects a callable, hence this thin wrapper function.
         def return_img(n):
-            return self.collection[n]
+            return self.images[n]
         assert_raises(IndexError, return_img, num)
         assert_raises(IndexError, return_img, -num - 1)
 
     def test_slicing(self):
-        assert type(self.collection[:]) is ImageCollection
-        assert len(self.collection[:]) == 2
-        assert len(self.collection[:1]) == 1
-        assert len(self.collection[1:]) == 1
-        assert_array_almost_equal(self.collection[0], self.collection[:1][0])
-        assert_array_almost_equal(self.collection[1], self.collection[1:][0])
-        assert_array_almost_equal(self.collection[1], self.collection[::-1][0])
-        assert_array_almost_equal(self.collection[0], self.collection[::-1][1])
+        assert type(self.images[:]) is ImageCollection
+        assert len(self.images[:]) == 2
+        assert len(self.images[:1]) == 1
+        assert len(self.images[1:]) == 1
+        assert_allclose(self.images[0], self.images[:1][0])
+        assert_allclose(self.images[1], self.images[1:][0])
+        assert_allclose(self.images[1], self.images[::-1][0])
+        assert_allclose(self.images[0], self.images[::-1][1])
 
     def test_files_property(self):
-        assert isinstance(self.collection.files, list)
+        assert isinstance(self.images.files, list)
 
         def set_files(f):
-            self.collection.files = f
+            self.images.files = f
         assert_raises(AttributeError, set_files, 'newfiles')
 
     def test_custom_load(self):
@@ -95,59 +79,12 @@ class TestImageCollection():
         assert_equal(ic[1], (2, 'two'))
 
     def test_concatenate(self):
-        ar = self.collection_matched.concatenate()
-        assert_equal(ar.shape, (len(self.collection_matched),) + 
-                                self.collection[0].shape)
-        assert_raises(ValueError, self.collection.concatenate)
+        array = self.images_matched.concatenate()
+        expected_shape = (len(self.images_matched),) + self.images[0].shape
+        assert_equal(array.shape, expected_shape)
 
-
-class TestMultiImage():
-
-    def setUp(self):
-        # This multipage TIF file was created with imagemagick:
-        # convert im1.tif im2.tif -adjoin multipage.tif
-        if PIL_available:
-            self.img = MultiImage(os.path.join(data_dir, 'multipage.tif'))
-
-    @skipif(not PIL_available)
-    def test_len(self):
-        assert len(self.img) == 2
-
-    @skipif(not PIL_available)
-    def test_getitem(self):
-        num = len(self.img)
-        for i in range(-num, num):
-            assert type(self.img[i]) is np.ndarray
-        assert_array_almost_equal(self.img[0],
-                                  self.img[-num])
-
-        #assert_raises expects a callable, hence this do-very-little func
-        def return_img(n):
-            return self.img[n]
-        assert_raises(IndexError, return_img, num)
-        assert_raises(IndexError, return_img, -num - 1)
-
-    @skipif(not PIL_available)
-    def test_files_property(self):
-        assert isinstance(self.img.filename, six.string_types)
-
-        def set_filename(f):
-            self.img.filename = f
-        assert_raises(AttributeError, set_filename, 'newfile')
-
-    @skipif(not PIL_available)
-    def test_conserve_memory_property(self):
-        assert isinstance(self.img.conserve_memory, bool)
-
-        def set_mem(val):
-            self.img.conserve_memory = val
-        assert_raises(AttributeError, set_mem, True)
-
-    @skipif(not PIL_available)
-    def test_concatenate(self):
-        ar = self.img.concatenate()
-        assert_equal(ar.shape, (len(self.img),) + 
-                                self.img[0].shape)
+    def test_concatentate_mismatched_image_shapes(self):
+        assert_raises(ValueError, self.images.concatenate)
 
 
 if __name__ == "__main__":
diff --git a/skimage/io/tests/test_image.py b/skimage/io/tests/test_image.py
index 6c54695b..b74c973e 100644
--- a/skimage/io/tests/test_image.py
+++ b/skimage/io/tests/test_image.py
@@ -1,7 +1,12 @@
-from skimage.io import Image
+from io import BytesIO
+
+import numpy as np
+from skimage import img_as_ubyte
+from skimage.io import Image, imread
 
 from numpy.testing import assert_equal, assert_array_equal
 
+
 def test_tags():
     f = Image([1, 2, 3], foo='bar', sigma='delta')
     g = Image([3, 2, 1], sun='moon')
@@ -11,7 +16,18 @@ def test_tags():
     assert_array_equal((g + 2).tags['sun'], 'moon')
     assert_equal(h.tags, {})
 
+
+def test_repr_png_roundtrip():
+    # Use RGB-like shape since some backends convert grayscale to RGB
+    original_array = 255 * np.ones((5, 5, 3), dtype=np.uint8)
+    image = Image(original_array)
+    array = imread(BytesIO(image._repr_png_()))
+    # Force output to ubyte range for plugin compatibility.
+    # For example, Matplotlib will return floats even if the image is uint8.
+    assert_array_equal(img_as_ubyte(array), original_array)
+    # Note that PIL breaks with `_repr_jpeg_`.
+
+
 if __name__ == "__main__":
     from numpy.testing import run_module_suite
     run_module_suite()
-
diff --git a/skimage/io/tests/test_io.py b/skimage/io/tests/test_io.py
index 8049860a..14879e64 100644
--- a/skimage/io/tests/test_io.py
+++ b/skimage/io/tests/test_io.py
@@ -4,6 +4,7 @@ from numpy.testing import assert_array_equal, raises, run_module_suite
 import numpy as np
 
 import skimage.io as io
+from skimage.io.manage_plugins import plugin_store
 from skimage import data_dir
 
 
@@ -28,5 +29,17 @@ def test_imread_url():
     assert image.shape == (512, 512)
 
 
+@raises(RuntimeError)
+def test_imread_no_plugin():
+    # tweak data path so that file URI works on both unix and windows.
+    image_path = os.path.join(data_dir, 'lena.png')
+    plugins = plugin_store['imread']
+    plugin_store['imread'] = []
+    try:
+        io.imread(image_path)
+    finally:
+        plugin_store['imread'] = plugins
+
+
 if __name__ == "__main__":
     run_module_suite()
diff --git a/skimage/io/tests/test_multi_image.py b/skimage/io/tests/test_multi_image.py
new file mode 100644
index 00000000..ebaa71dc
--- /dev/null
+++ b/skimage/io/tests/test_multi_image.py
@@ -0,0 +1,69 @@
+import os
+
+import numpy as np
+from numpy.testing.decorators import skipif
+from numpy.testing import assert_raises, assert_equal, assert_allclose
+
+from skimage import data_dir
+from skimage.io.collection import MultiImage
+
+try:
+    from PIL import Image
+except ImportError:
+    PIL_available = False
+else:
+    PIL_available = True
+
+import six
+
+
+class TestMultiImage():
+
+    def setUp(self):
+        # This multipage TIF file was created with imagemagick:
+        # convert im1.tif im2.tif -adjoin multipage.tif
+        if PIL_available:
+            self.img = MultiImage(os.path.join(data_dir, 'multipage.tif'))
+
+    @skipif(not PIL_available)
+    def test_len(self):
+        assert len(self.img) == 2
+
+    @skipif(not PIL_available)
+    def test_getitem(self):
+        num = len(self.img)
+        for i in range(-num, num):
+            assert type(self.img[i]) is np.ndarray
+        assert_allclose(self.img[0], self.img[-num])
+
+        # assert_raises expects a callable, hence this thin wrapper function.
+        def return_img(n):
+            return self.img[n]
+        assert_raises(IndexError, return_img, num)
+        assert_raises(IndexError, return_img, -num - 1)
+
+    @skipif(not PIL_available)
+    def test_files_property(self):
+        assert isinstance(self.img.filename, six.string_types)
+
+        def set_filename(f):
+            self.img.filename = f
+        assert_raises(AttributeError, set_filename, 'newfile')
+
+    @skipif(not PIL_available)
+    def test_conserve_memory_property(self):
+        assert isinstance(self.img.conserve_memory, bool)
+
+        def set_mem(val):
+            self.img.conserve_memory = val
+        assert_raises(AttributeError, set_mem, True)
+
+    @skipif(not PIL_available)
+    def test_concatenate(self):
+        array = self.img.concatenate()
+        assert_equal(array.shape, (len(self.img),) + self.img[0].shape)
+
+
+if __name__ == "__main__":
+    from numpy.testing import run_module_suite
+    run_module_suite()
diff --git a/skimage/io/tests/test_null.py b/skimage/io/tests/test_null.py
new file mode 100644
index 00000000..6d3913d9
--- /dev/null
+++ b/skimage/io/tests/test_null.py
@@ -0,0 +1,35 @@
+import os
+import warnings
+
+import numpy as np
+from numpy.testing import raises
+
+from skimage import io
+from skimage import data_dir
+
+
+@raises(Warning)
+def test_null_imread():
+    path = os.path.join(data_dir, 'color.png')
+    with warnings.catch_warnings():  # Temporarily set warnings as errors.
+        warnings.filterwarnings('error')
+        io.imread(path, plugin='null')
+
+
+@raises(Warning)
+def test_null_imsave():
+    with warnings.catch_warnings():  # Temporarily set warnings as errors.
+        warnings.filterwarnings('error')
+        io.imsave('dummy.png', np.zeros((3, 3)), plugin='null')
+
+
+@raises(Warning)
+def test_null_imshow():
+    with warnings.catch_warnings():  # Temporarily set warnings as errors.
+        warnings.filterwarnings('error')
+        io.imshow(np.zeros((3, 3)), plugin='null')
+
+
+if __name__ == '__main__':
+    from numpy.testing import run_module_suite
+    run_module_suite()
diff --git a/skimage/io/tests/test_plugin.py b/skimage/io/tests/test_plugin.py
index 5d1febe4..06f3a600 100644
--- a/skimage/io/tests/test_plugin.py
+++ b/skimage/io/tests/test_plugin.py
@@ -1,7 +1,9 @@
-from numpy.testing import *
+from contextlib import contextmanager
+
+from numpy.testing import assert_equal, raises
 
 from skimage import io
-from skimage.io._plugins import plugin
+from skimage.io import manage_plugins
 from numpy.testing.decorators import skipif
 
 try:
@@ -19,70 +21,115 @@ except RuntimeError:
     FI_available = False
 
 
-def setup_module(self):
-    plugin.use('test')  # see ../_plugins/test_plugin.py
+def setup_module():
+    manage_plugins.use_plugin('test')  # see ../_plugins/test_plugin.py
 
 
-def teardown_module(self):
+def teardown_module():
     io.reset_plugins()
 
 
-class TestPlugin:
-    def test_read(self):
-        io.imread('test.png', as_grey=True, dtype='i4', plugin='test')
+@contextmanager
+def protect_preferred_plugins():
+    """Contexts where `preferred_plugins` can be modified w/o side-effects."""
+    preferred_plugins = manage_plugins.preferred_plugins.copy()
+    try:
+        yield
+    finally:
+        manage_plugins.preferred_plugins = preferred_plugins
 
-    def test_save(self):
-        io.imsave('test.png', [1, 2, 3], plugin='test')
 
-    def test_show(self):
-        io.imshow([1, 2, 3], plugin_arg=(1, 2), plugin='test')
+def test_read():
+    io.imread('test.png', as_grey=True, dtype='i4', plugin='test')
 
-    def test_collection(self):
-        io.imread_collection('*.png', conserve_memory=False, plugin='test')
 
-    def test_use(self):
-        plugin.use('test')
-        plugin.use('test', 'imshow')
+def test_save():
+    io.imsave('test.png', [1, 2, 3], plugin='test')
 
-    @raises(ValueError)
-    def test_failed_use(self):
-        plugin.use('asd')
 
-    @skipif(not PIL_available and not FI_available)
-    def test_use_priority(self):
-        plugin.use(priority_plugin)
-        plug, func = plugin.plugin_store['imread'][0]
-        assert_equal(plug, priority_plugin)
+def test_show():
+    io.imshow([1, 2, 3], plugin_arg=(1, 2), plugin='test')
 
-        plugin.use('test')
-        plug, func = plugin.plugin_store['imread'][0]
-        assert_equal(plug, 'test')
 
-    @skipif(not PIL_available)
-    def test_use_priority_with_func(self):
-        plugin.use('pil')
-        plug, func = plugin.plugin_store['imread'][0]
-        assert_equal(plug, 'pil')
+def test_collection():
+    io.imread_collection('*.png', conserve_memory=False, plugin='test')
 
-        plugin.use('test', 'imread')
-        plug, func = plugin.plugin_store['imread'][0]
-        assert_equal(plug, 'test')
 
-        plug, func = plugin.plugin_store['imsave'][0]
-        assert_equal(plug, 'pil')
+def test_use():
+    manage_plugins.use_plugin('test')
+    manage_plugins.use_plugin('test', 'imshow')
 
-        plugin.use('test')
-        plug, func = plugin.plugin_store['imsave'][0]
-        assert_equal(plug, 'test')
 
-    def test_plugin_order(self):
-        p = io.plugin_order()
-        assert 'imread' in p
-        assert 'test' in p['imread']
+@raises(ValueError)
+def test_failed_use():
+    manage_plugins.use_plugin('asd')
+
+
+@skipif(not PIL_available and not FI_available)
+def test_use_priority():
+    manage_plugins.use_plugin(priority_plugin)
+    plug, func = manage_plugins.plugin_store['imread'][0]
+    assert_equal(plug, priority_plugin)
+
+    manage_plugins.use_plugin('test')
+    plug, func = manage_plugins.plugin_store['imread'][0]
+    assert_equal(plug, 'test')
+
+
+@skipif(not PIL_available)
+def test_use_priority_with_func():
+    manage_plugins.use_plugin('pil')
+    plug, func = manage_plugins.plugin_store['imread'][0]
+    assert_equal(plug, 'pil')
+
+    manage_plugins.use_plugin('test', 'imread')
+    plug, func = manage_plugins.plugin_store['imread'][0]
+    assert_equal(plug, 'test')
+
+    plug, func = manage_plugins.plugin_store['imsave'][0]
+    assert_equal(plug, 'pil')
+
+    manage_plugins.use_plugin('test')
+    plug, func = manage_plugins.plugin_store['imsave'][0]
+    assert_equal(plug, 'test')
+
+
+def test_plugin_order():
+    p = io.plugin_order()
+    assert 'imread' in p
+    assert 'test' in p['imread']
+
+
+def test_available():
+    assert 'qt' in io.available_plugins
+    assert 'test' in io.find_available_plugins(loaded=True)
+
+
+def test_load_preferred_plugins_all():
+    from skimage.io._plugins import null_plugin
+
+    with protect_preferred_plugins():
+        manage_plugins.preferred_plugins = {'all': ['null']}
+        manage_plugins.reset_plugins()
+
+        for plugin_type in ('imread', 'imsave', 'imshow'):
+            plug, func = manage_plugins.plugin_store[plugin_type][0]
+            assert func == getattr(null_plugin, plugin_type)
+
+
+def test_load_preferred_plugins_imread():
+    from skimage.io._plugins import null_plugin
+
+    with protect_preferred_plugins():
+        manage_plugins.preferred_plugins['imread'] = ['null']
+        manage_plugins.reset_plugins()
+
+        plug, func = manage_plugins.plugin_store['imread'][0]
+        assert func == null_plugin.imread
+        plug, func = manage_plugins.plugin_store['imshow'][0]
+        assert func != null_plugin.imshow
 
-    def test_available(self):
-        assert 'qt' in io.plugins()
-        assert 'test' in io.plugins(loaded=True)
 
 if __name__ == "__main__":
+    from numpy.testing import run_module_suite
     run_module_suite()
diff --git a/skimage/io/util.py b/skimage/io/util.py
new file mode 100644
index 00000000..06f5a5b5
--- /dev/null
+++ b/skimage/io/util.py
@@ -0,0 +1,36 @@
+try:
+    from urllib.request import urlopen  # Python 3
+except ImportError:
+    from urllib2 import urlopen  # Python 2
+
+import os
+import re
+import tempfile
+from contextlib import contextmanager
+
+from skimage._shared import six
+
+
+URL_REGEX = re.compile(r'http://|https://|ftp://|file://|file:\\')
+
+
+def is_url(filename):
+    """Return True if string is an http or ftp path."""
+    return (isinstance(filename, six.string_types) and
+            URL_REGEX.match(filename) is not None)
+
+
+@contextmanager
+def file_or_url_context(resource_name):
+    """Yield name of file from the given resource (i.e. file or url)."""
+    if is_url(resource_name):
+        _, ext = os.path.splitext(resource_name)
+        with tempfile.NamedTemporaryFile(delete=False, suffix=ext) as f:
+            u = urlopen(resource_name)
+            f.write(u.read())
+        try:
+            yield f.name
+        finally:
+            os.remove(f.name)
+    else:
+        yield resource_name