I used stock photographs in a "multimedia" game I produced 15 years ago. I've seen WWII games that used stock photos from that era.
There sometimes might be a need for new photos to be taken, of costumed characters or of landscapes or city scenes. But these days with the graphics capabilities of game hardware, they might prefer to simply create something (even though it could be cheaper to use a photographer's services instead).

To make yourself known in the game industry, you can post an announcement about your availability here in our Help Wanted board, you can build a website and make sure to tag lots of pages and photos with "game" terms, but mainly what you need to do is network. Go to conventions and conferences, take photos there, get some of your work used in some indie games.

Scroll up and look for the tiny blue "View Forum FAQ" link and click it. There's a section in there about networking and freelancing.