At the moment I've decided not to work from digital images.
I feel I need to get a firm hold of Alla Prima before resorting to digital pics.
One needs to be able to transcribe what one sees into colors, values, the right hue, saturation. Only when I feel I have a firm grasp of that, will I paint directly from digital images.
Working from digital photos makes the job of placing the hues much simpler, although some would disagree. It all depends on one's own style of seeing things. How much you can train yourself into recognizing the values and colors from life.
Its a nice habit to look around , frame a picture of what you see in your mind, then turn it into a painting,(in your mind), first trying to see it in a monochoromatic tone, then as pigments. Then make a color menu out of it. Nice habit to keep!
Blurring your eyes will help a lot. Carry around a camera, or if you use a mobile phone with a camera, keep clicking away, then come back to your favourite image editor, and experiment with the tones and colors. You can call it your digital sketch book. Archive it regularly , soon you will have a library of your own images.