This is one I'd been thinking about for awhile but finally go around to giving it a shot. I made Tesla some custom coloring book pages using photos of people in her life: herself, Mie and I, Elida, Sofia, MIchelle and Jeremy (and their new cat Francis). I figure coloring people she knows should be more fun than coloring random fictional princesses and mermaids right?
The process is simple: pull the original photo up in Photoshop and create a new layer. Use the brush tool to trace the original images in the new layer and the layer panel to hide/show the original as needed to check the work. It's about 5 minutes per photo.