All of my art is made using various editing apps on the iPhone. Much akin to photoshop style workflow, I go from app to app adding to the process. For example this image was made out of a profile shot of my friend Wayman wearing a Viking helmet.
I used apps for mirroring, apps to add painterly effects, and layering apps to "cut" out the face to add to the bottom. I also enjoy hiding images within my work. (Hold the image away from your face and you can see a Minotaur looking you in the eyes)