Lyra Cellucolor pencils, which are formulated for use on slick surfaces like plastic and china. I discovered them while hunting for something that would work on playing cards (which have a plastic coating), and found they also work beautifully on photo paper. They are hard to find, and the link is to the only US source I know.
This is a scan of the finished photo-drawing. The original is in my etsy shop. (Clicking on the photo will take you to the listing.)