Some of the image thumbnails I’ve put into posts have stopped displaying. I obviously put them in there at some point, but somehow the link has been broken. When I replace it I get a different url, not sure why! I use the same process to insert it (‘add an image’ from the toolbar).
You haven’t perchance deleted those files from the Media Library, have you? There’s some dope going around pretending he knows what he’s doing, who tells people to do that. Obviously, if you delete them from the Media Library, you’ve deleted them from your blog as well.