I am against it as I can not see any real use for it. As Footed PJ Says, there is a report button for images that break the rules.
There is no image I feel should get any +ve or -Ve rep. Majority of the pictures are usually random and don't really contribute to the whole supporting factor of this site. So the rep system will have no use otherwise.
"Thanks your cute too"
"wowwwwwww cant believe you called me that"
"your pic disgusts me"
"your so hot"
"i love you your so cute"
Who gives rep for that?
And IIRC rep on blogs was brought up, and it was basically concluded that if you found a blog REALLY deserved a rep, then find a post by that person and use that to rep them. If something in the gallery REALLY deserves rep, then use the same method. Find a post and rep them there for it.
Mandi's right - people would mostly use it to rate the person in the picture, not the picture itself. Posting a boring picture of some hot-looking person would get you positive rep, posting an artistic shot of an ugly person most likely not. I don't think we want reputation to become a beauty contest!
Meh- what I originally meant was for the comments, like if some one was harassing you, you could report and neg-rep, just like in the forums. I thought it might be something to discourage unwanted comments like, "hiya, sweetass" or something like that.