title: Unable to pickle complete dataset
body: <p>I am currently working on an assignment in the Udacity Deep Learning Course which follows <a href="https://github.com/tensorflow/tensorflow/blob/master/tensorflow/examples/udacity/1_notmnist.ipynb" rel="nofollow">this IPython Notebook</a>. When  I try to pickle the datasets (function <code>maybe_pickle</code>), it is able to pickle up to the folder "F", but no further. This is the output I am getting.</p>
  
  <pre><code>['././notMNIST_large/A', '././notMNIST_large/B', '././notMNIST_large/C', '././notMNIST_large/D', '././notMNIST_large/E', '././notMNIST_large/F', '././notMNIST_large/G', '././notMNIST_large/H', '././notMNIST_large/I', '././notMNIST_large/J']
  Pickling ././notMNIST_large/A.pickle
  ././notMNIST_large/A
  Could not read  ././notMNIST_large/A/Um9tYW5hIEJvbGQucGZi.png  :  cannot identify image file '././notMNIST_large/A/Um9tYW5hIEJvbGQucGZi.png' 
  Skipping this image.
  Could not read  ././notMNIST_large/A/RnJlaWdodERpc3BCb29rSXRhbGljLnR0Zg==.png  :  cannot identify image file '././notMNIST_large/A/RnJlaWdodERpc3BCb29rSXRhbGljLnR0Zg==.png' 
  Skipping this image.
  Could not read  ././notMNIST_large/A/SG90IE11c3RhcmQgQlROIFBvc3Rlci50dGY=.png  :  cannot identify image file '././notMNIST_large/A/SG90IE11c3RhcmQgQlROIFBvc3Rlci50dGY=.png' 
  Skipping this image.
  Full dataset tensor:  (52909, 28, 28)
  Mean:  -0.12825
  Standard Deviation:  0.443121
  Pickling ././notMNIST_large/B.pickle
  ././notMNIST_large/B
  Could not read  ././notMNIST_large/B/TmlraXNFRi1TZW1pQm9sZEl0YWxpYy5vdGY=.png  :  cannot identify image file '././notMNIST_large/B/TmlraXNFRi1TZW1pQm9sZEl0YWxpYy5vdGY=.png' 
  Skipping this image.
  Full dataset tensor:  (52911, 28, 28)
  Mean:  -0.00756303
  Standard Deviation:  0.454492
  Pickling ././notMNIST_large/C.pickle
  ././notMNIST_large/C
  Full dataset tensor:  (52912, 28, 28)
  Mean:  -0.142258
  Standard Deviation:  0.439806
  Pickling ././notMNIST_large/D.pickle
  ././notMNIST_large/D
  Could not read  ././notMNIST_large/D/VHJhbnNpdCBCb2xkLnR0Zg==.png  :  cannot identify image file '././notMNIST_large/D/VHJhbnNpdCBCb2xkLnR0Zg==.png' 
  Skipping this image.
  Full dataset tensor:  (52911, 28, 28)
  Mean:  -0.0573678
  Standard Deviation:  0.455647
  Pickling ././notMNIST_large/E.pickle
  ././notMNIST_large/E
  Full dataset tensor:  (52912, 28, 28)
  Mean:  -0.0698991
  Standard Deviation:  0.452942
  Pickling ././notMNIST_large/F.pickle
  ././notMNIST_large/F
  Full dataset tensor:  (52912, 28, 28)
  Mean:  -0.125583
  Standard Deviation:  0.447089
  Pickling ././notMNIST_large/G.pickle
  ././notMNIST_large/G
  </code></pre>
  
  <p>Nothing happens after this, i.e. it never terminates. Any ideas on how to proceed? I have even tried terminating the program and running it again but there has been no progress.</p>