This patch is for Gallery v2.3.1.
While attempting to add an image RSS feed to my Google Profile, I noticed that all the images in the widget were 'clickable' but not showing their respective thumbnails. Digging a bit deeper, it appeared that when using Media RSS tags, the thumbnail URL was being set to the actual link within the gallery, and not the img src link.
I searched through the bug entries, and found <a target="_blank" href="https://sourceforge.net/tracker/index.php?func=detail&aid=2541381&group_id=7130&atid=107130">Bug #: 2541381</a> which was opened for the same issue. I wasn't sure if bubbawilson's fix was correct, so I came up with my own which made the change in RssGenerator.class, instead of RssHelper.class
In addition to fixing the image URL, I also added the image type which was missing.
After applying the fix, and testing it, the Google widget showed the correct thumbnail image, and once clicked, brought me to the correct gallery link for the full image.