You can put anything you want in a provisional application. Photos (even color photos) are frequently filed in regular utility applications too, but they don't reproduce well, so examiners will often require you to submit line drawings. (Still, a fair number of patents issue with crappy, hard-to-see photos, so it's not a guarantee that you'll have to do anything.)
The most important thing is that the photos (or drawings or whatever) clearly show whatever part of the invention you're trying to show. If they don't, you may get stuck in a "new matter" trap: you have to submit new drawings, but you're not allowed to do so because your original drawings don't show everything, which means you (presumably) didn't have "possession" of the invention on your filing date.
The drawings and description must do at least two things: teach a person of ordinary skill how to make or use your invention; and prove that you were able to make or use your invention, on the date you filed the application. If you have any hand-waving in there, it looks like you didn't really know how to do what you're claiming you could do.