As a digital artist, I can say that some form of digital art are closer to photography than others.
Generative art is one: you choose to fix a moment and a view of the generative process on an image... that's what the photographer does with the real world.
Another one is 3d animation : you setup your camera to take photos of your virtual set.
I would say the the photographer creates art by choosing what to frame and enclose in a picture, while, in other art forms, you choose what to frame starting only from your visions.
But again, painting is a technique born to recreate the nature..
So, i guess, the difference, if any, is extremely tight, and varies in time.. Is more a matter of strict definition than anything else..