I just read again the adsense guideline: No Google ad may be placed on any non-content-based pages. I put ad on a gallery page. That page is to show pictures uploaded by users. So the page are photos only. Is that against the guideline? And i saw another guideline: No Google ad or Google search box may be displayed on any domain parking websites, pop-ups, pop-unders, or in any email. But Godday domain packing sites are full of adsense ad if i remember correctly. I once registered a domain name but not having name server set up yet. So if you type my domain name, you'll go to a page which says "this domain is parked on godaddy.com by courtesy ..." and having some google adsense ads on that page... And also, there are a lot of sites just some misspelling domain name of other popular domains. When you typed a domain with typo, it'll take you to a site which has adsense ad only... how come those are not banned?
They are special publishers, doing what they want with the ads, dont worry about them. Now, images are content as far as I can judge.
That's a good question, I've wondered that myself. As far as ads on a gallery page, that wouldn't likely be against the TOS simply because they don't state that the content has to be textual. Images, video, and other types of files are content too. However, Google might view it differently, but I haven't had any problems with it so far, and I have a great deal of pages with very little textual content.
As someone with 13,000+ images on a comic-covers site (ahem), I can tell you that adsense is just fine with the images hosted at your site. BUT... I believe there might be something in the TOS against putting ads on 'image results,' which I take to mean pages generated according to users' searches, or something similar. If your site is an image hosting site, as it sounds like, you should be okay.