When I take photographs, I try to compose my subjects the best I can in the lens then back in the studio, half the difficulty in painting has been resolved. I find it much better than struggling to rearrange a composition that wasn't quite right in the photo. With a good photograph I'll more likely end up with a good painting.
I sometimes capture a still image from my video cameras as well. I've been able to capture images that are quite suffecient to use as reference.