I wonder why the Google image search finds my thumbs (size on articles) but not the full images. When I search the unique file name from the URL and go for "more sizes" only the thumb is found.
As if the crawler doesn't follow the thumb link to the file page (where it could grab the link to the full image URL).
My robots.txt doesn't disallow the File ns.
Also the XML sitemap includes the File ns and Google Webmaster Tools throws no errors.