diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index fd7cb005..d5db0f5c 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -84,7 +84,12 @@ class Plugin(QtGui.QDialog):
         arguments = [self._get_value(a) for a in self.arguments]
         kwargs = dict([(name, self._get_value(a))
                        for name, a in self.keyword_arguments.iteritems()])
-        self.image_filter(*arguments, **kwargs)
+        filtered = self.image_filter(*arguments, **kwargs)
+        self.display_filtered_image(filtered)
+
+    def display_filtered_image(self, image):
+        """Override this method to display image on image viewer."""
+        pass
 
     def _get_value(self, param):
         return param if not hasattr(param, 'val') else param.val()
@@ -102,6 +107,9 @@ class Plugin(QtGui.QDialog):
         self.layout.addWidget(widget, self.row, 0)
         self.row += 1
 
+    def __iadd__(self, widget):
+        self.add_widget(widget)
+
     def update_plugin(self, name, value):
         setattr(self, name, value)
 
diff --git a/skimage/viewer/plugins/canny.py b/skimage/viewer/plugins/canny.py
index b161fd87..154fb6da 100644
--- a/skimage/viewer/plugins/canny.py
+++ b/skimage/viewer/plugins/canny.py
@@ -9,7 +9,7 @@ class CannyPlugin(OverlayPlugin):
     name = 'Canny Filter'
 
     def __init__(self, *args, **kwargs):
-        super(CannyPlugin, self).__init__(**kwargs)
+        super(CannyPlugin, self).__init__(image_filter=canny, **kwargs)
 
         self.add_widget(Slider('sigma', 0, 5, update_on='release'))
         self.add_widget(Slider('low threshold', 0, 255, update_on='release'))
@@ -20,7 +20,3 @@ class CannyPlugin(OverlayPlugin):
         super(CannyPlugin, self).attach(image_viewer)
         # Update image overlay to default slider values.
         self.filter_image()
-
-    def image_filter(self, *args, **kwargs):
-        image = canny(*args, **kwargs)
-        self.overlay = image
diff --git a/skimage/viewer/plugins/overlayplugin.py b/skimage/viewer/plugins/overlayplugin.py
index 3b051e1a..3aa5a445 100644
--- a/skimage/viewer/plugins/overlayplugin.py
+++ b/skimage/viewer/plugins/overlayplugin.py
@@ -45,6 +45,10 @@ class OverlayPlugin(Plugin):
             self._overlay_plot.set_array(image)
         self.image_viewer.redraw()
 
+    def display_filtered_image(self, image):
+        """Display image over image in viewer."""
+        self.overlay = image
+
     def closeEvent(self, event):
         self.overlay = None
         super(OverlayPlugin, self).closeEvent(event)