If you want to see thumbnails of your pictures in explorer do the following:

  1.  Click the "View" tab in explorer and you will see this menu: 

    2. Highlight the "Large icons" option and close the tab again. 

Note that this will cause all pictures to be downloaded and stored locally!

If you still do not see any thumbnails do the following:

  1. Click the "View" tab in explorer.
  2. Click the "Options" button on the right and go the "View" tab. 

  3. Make sure the "Always show icons, never thumbnails" option is NOT marked.