Selected answers from the Dumb SEO Questions G+ community.
Michael Martinez: Image page optimization isn`t much different from optimizing a page full of text. The thing is, the search engines still have only limited capabilities for identifying what is IN the images (and then those capabilities are only used in the Image Search indexes, so far as I know).
It depends on a lot of things, including (but not limited to):
1) How long it takes the page to load and render (extremely slow pages will be scored lower).
2) How relevant the image filenames and annotations (ALT= text, captions), are to any queries.
3) How relevant any other copy on the page is to any queries.
4) How much PageRank-like value the page receives from (both external and internal) links.
5) How clearly defined the objects the images are about tend to be. i.e., if it`s a picture of a chair, is it obvious enough for AI algorithms to see that it`s a chair and not a folding table?
Fernanda Herrera: thank you, and if all of the above is optimize does it change if I have 1 photo or 5 photos in an article?
Michael Martinez: I would say the page would be potentially more relevant for more queries with 5 photos than 1. As for whether 5 photos about the same topic would improve relevance scoring, your guess is as good as mine.
Intuitively, I believe the search engines want to show a more robust result if they can - so 5 photos versus 1 might be better. But what if the 1 photo is singular in some way?
This is something that requires experimentation, and I would not expect an experiment to produce the same results for everyone.