[Kitten]

I would like to report them, yeah. Or at least call them out on it. I don't know what the mods stance on it is though, and you might be banned/warned yourself for harassment, before the person with a fake picture is banned/warned for being misleading or broaching copyrights.
If they have playpartners that are friends or good acquaintances of mine I do "rat them out" though. Just because I don't want genuine/serious people being tricked or even hurt for no real reason.

Edit; I do mean when they use pictures and pretend or say it's them, when it's really not. Of course, if people just use a picture that they feel represents them in some way it's a completely different matter.