I just completed a new digital painting which is posted above. This is a digital painting based on an image I took with my new IPhone 7s at the grocery store, of all places. I have found that IPhone images can make great photo paintings. The painting process can eliminate any defects like noise which often occur in IPhone images, and the image can be resized with impunity if it is then painted. Again, the painting process will correct all defects associated with the upsizing. I like the freedom and spontaneity that shooting with an IPhone brings to the table, and so I will undoubtedly be using that camera more and more for my photo paintings.
Before I start the painting process in Procreate, I usually process the image some on my IPhone. In this case I used Snapseed and Prisma before bringing it into Procreate. This processing is meant to bring up the colors in the image and to simplify it to some extent. I have found that I like highly saturated images and that those usually look best when painted. Also, painted images usually are not as detailed as photos, and so some simplification of the image is necessary before painting.