Hi Stephen,
Hope you are enjoying the forum!
You raise some rather interesting questions regarding photography and copyright which I think we all could explore further. The main issue regarding breach of copyright is - to what extent does the final (secondary) work (the painting or drawing, for instance) rely on the photograph (the primary resource).
If I were to apishly copy a copyrighted photograph (without the consent of the photographer) where the result was, in fact, simply a hand-rendered version of the original, then I may well have breached copyright and find myself open to litigation.
If, however, I use several photographs FOR REFERENCE (for instance, checking the iris colour on a short-eared owl, the extent of barring on it's secondaries, etc) then it's unlikely to be an issue.
Using photographic reference isn't illegal, regardless of who took the photograph. What is against the law, immoral AND totally uncreative is the slavish copying of a single photographic image, simply to re-title that image as a painting.
Therefore I heartily recomment one doesn't do it. (the results are ALWAYS screamingly obvious - in colour, tonal value, perspective and lighting, in fact, everything a work of art ought not to be.
Art = originality.
I'm sure others will comment, but I'd really like to hear from Andy (Bright) on this issue. He's far more of an expert and will have an invaluable contribution to make - for you and the rest of us.
If you're reading, Andy? . . .