I like drawing realistic portraits. Working from life is fun,

>>2707898
If you can't make your portrait from life, at least sit together and make a number of sketches, studies... photograph from different angles...

>>2707898
do both as much as possible so that you can learn how to interpret what the photo is saying in your own visual way.

A well taken photograph usually accounts for a lot of the issues, but if you're studying from pictures and selfies snapped from camera phones you're going to have some problem.

>>2707898
>but I keep reading about things like lens distortion, value compression, and colour inaccuracy.
Those are things that matter to photographers, not artists.
Either you're trying to draw something exactly as you see it, in which case you draw something with the effects of the camera included
Or you're trying to draw something in such a way it's exaggerated (focus on values, lines, etc) so the camera's effects don't matter because your hand as an artist is far heavier

Artists worry and piddle about every little thing all the time, that's normal. If you want a camera get one, there are no references better than the ones you collect yourself because they're taken in such a way that focus on what you need the reference for.