It's the strangest thing, I have pictures that I copy/paste that do not show in my thumbnails (while others show). The images are viewable just fine within the note, but does not show in the thumbnails. I like everything to be consistent so this makes me crazy. I can't figure out WHY it happens, but it must be something with the way the picture is copied/pasted. Because, the FIX I have found is to download the image (from my saved Evernote) onto my computer. Then I delete the image from my Note, and I re-add it from the saved version on my computer. THEN and only then does it seem to upload into the thumbnail.