Well it's been three years and this still isn't implemented and Evernote continues to pick the wrong thumbnail. So is this going to be fixed any time soon? I can't even seem to cut/copy an image from Evernote and paste it into an image editing program, so perhaps that can be fixed too. Seems odd to have a native app that fails the basic rules for a native app.
I have read some posts regarding how Evernote 'decides' to select the thumbnail image to show on notes and I still do not understand why I cannot override this behavior by clicking on an image in a note and selecting "Assign Thumbnail". Until this is done I cannot pay money for Evernote as Springpad managed to get this working. Even with this automatic method, Evernote PC vs Web vs Android do different things. On the PC I somehow managed to get the thumbnails that I wanted showing by cut/sync/pasting until it worked (highly annoying). Then I go to view my notes on the Web or Android client