It will void your warranty, but I think your best (if not your only) bet will be to pop open the AppleTV, take out the hard drive, get a 2.5'' HDD adapter, and plug it into your computer. Once you do that, you will find something that looks not to dissimilar to an OSX install on the AppleTV's hard drive, and you should be able to use the finder to locate your photos.
I believe if the computer syncs with the AppleTV in the normal fashion, and the computer lacks the files that are on the AppleTV, it will erase those files from the device.