I normally spray inkjet prints with a UV filter spray as it also provides some mechanical protection and helps reduce ffinger prints.
Last week I had some marks on a print -- could have been fingerprints -- and found that an extra spray coat made them invisible.
If you can't find any better way of removing the prints then it's worth a try. A good quality UV spray will be totally invisible so it won't make the marks any worse, and it might just make them invisible.
I've also tried removing marks from inkjet prints with 3M art cleaner, with soft erasers, soapy water and with putty-type art cleaner. In almost all cases they have made things much worse and have usually destroyed the print. Some inkjet prints are OK with some methods but you need to know about both the ink and the substrate to be able to judge.
Real photographs, on the other hand, are generally water proof but it's best to use distilled water to avoid any residues. Don't forget, real photographs are produced under water (with chemicals) and copiously washed as the final process.
