There are no rules against that but with no text you may get public service announcements only as AdSense bot cannot determine what your content is.
I think it's a bit risky. It would depend on the quality of your blog. Also, there is a risk in having ads lined up with images, or too close to images. That can be a red flag. You might want to have your layout reviewed. Adding text content would be wise.
Adsense is a context advetisement. It means that there must be some text in the site page. From webmasters guidelines: "Try to use text instead of images to display important names, content, or links. The Google crawler doesn't recognize text contained in images...No Google ad may be placed on any non-content-based pages. "
Not really a rule, more of a technical impossibility since image-recognition isn't all that good yet. As for not having adsense on a non-content page, I don't know if I would consider an image gallery a content-less page (a picture is worth a thousand words, afterall, lol) However, one thing that I would do is put a caption for the picture. Surely you aren't going to just to an "image dump" Describe the photo, otherwise SE traffic may not be that spectacular. If they are _your_ images, you should be able to say where they are from, when they were taken, etc. If they are NOT your images, then there is a rule about copyrighted material... (yes, another doggone rule lol)