They usually get converted to attachment links. You can just re-post actual pics to the ad, I usually do.
But, they usually (and annoyingly) re-post at the very top of the ad, above the text, rather than after it, like they do with a fresh ad. Not sure why the whole process is so quirky, but whatcha gonna do?
Yeah, I just bump, then zap the links, and post fresh pics. If you have to relist entirely, at least you can copy/paste all the text, so it isn't very time consuming.