I do pencil sketches, so I have to practice from people.
(Clothed preferably as that also gives me practice with shading folds of cloth rather than folds of flubb.. er.. skin. Costumed would be even better if close to the idea in my head.)
I'm terrible with photography.
There's a big difference between drawing an idealized nude woman, and drawing a 30-year-old, 200 lbs., nude woman. If you produce a representative image of the latter, you can really draw.
I've done some good photos of cats, but babies don't pose as nicely!