Added sections to gallery of examples

Modified travis_script.sh to account for the new structure of the gallery

Added README.txt files in directories of gallery examples

Fixed references to gallery images in user guide pages

Fixed broken links

doc/examples/segmentation/plot_local_otsu.py

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+"""
+====================
+Local Otsu Threshold
+====================
+
+This example shows how Otsu's threshold [1]_ method can be applied locally. For
+each pixel, an "optimal" threshold is determined by maximizing the variance
+between two classes of pixels of the local neighborhood defined by a
+structuring element.
+
+The example compares the local threshold with the global threshold.
+
+.. note: local is much slower than global thresholding
+
+.. [1] http://en.wikipedia.org/wiki/Otsu's_method
+
+"""
+import matplotlib
+import matplotlib.pyplot as plt
+
+from skimage import data
+from skimage.morphology import disk
+from skimage.filters import threshold_otsu, rank
+from skimage.util import img_as_ubyte
+
+
+matplotlib.rcParams['font.size'] = 9
+
+
+img = img_as_ubyte(data.page())
+
+radius = 15
+selem = disk(radius)
+
+local_otsu = rank.otsu(img, selem)
+threshold_global_otsu = threshold_otsu(img)
+global_otsu = img >= threshold_global_otsu
+
+
+fig, ax = plt.subplots(2, 2, figsize=(8, 5), sharex=True, sharey=True, subplot_kw={'adjustable':'box-forced'})
+ax1, ax2, ax3, ax4 = ax.ravel()
+
+fig.colorbar(ax1.imshow(img, cmap=plt.cm.gray),
+             ax=ax1, orientation='horizontal')
+ax1.set_title('Original')
+ax1.axis('off')
+
+fig.colorbar(ax2.imshow(local_otsu, cmap=plt.cm.gray),
+             ax=ax2, orientation='horizontal')
+ax2.set_title('Local Otsu (radius=%d)' % radius)
+ax2.axis('off')
+
+ax3.imshow(img >= local_otsu, cmap=plt.cm.gray)
+ax3.set_title('Original >= Local Otsu' % threshold_global_otsu)
+ax3.axis('off')
+
+ax4.imshow(global_otsu, cmap=plt.cm.gray)
+ax4.set_title('Global Otsu (threshold = %d)' % threshold_global_otsu)
+ax4.axis('off')
+
+plt.show()