Can I turn a photo into a coloring page?
Yes. The cleanest way is to trace it: put the photo on a separate layer, draw the main outlines on top with a thick brush, then hide the photo and export only the lines.
Automatic "photo to sketch" filters tend to produce grey, broken lines and lots of tiny noise, which is frustrating to color. Tracing by hand gives bold closed shapes in a few minutes.
On a tablet: import the photo, lower its opacity to about 30%, add a new layer, and trace the outlines you care about with a 6–10 px brush. Skip textures like hair strands or grass blades; one outline for each area is enough.
On paper: print the photo lightly, lay a sheet of copy paper over it on a window or a light box, and trace with a black marker. Then scan the tracing.
