Google does all kinds of things to determine page rankings. They don't use keywords as much as in the past, since they have become so adept at determining a page's true value to the web user. If you want your photos to be found in a search, go ahead and put in the keywords, but you should also include these words in descriptive text throughout the page.
The most important thing to quality Google rankings these days seems to be to get popular sites to link to your page. For instance, if cnn.com did an article about your images and linked to your page, your rank would bump up significantly. It's too easy to fake keywords, etc, and Google has a remarkable knack for digging through the crap on the web.