I haven't checked the actual web-site as I don't use Photoshop, but I love the effect and can see me using this myself. Where I pinned it from said "How to Create a "Double Exposure" in Photoshop — Daily Epiphanie"
Portland-based photographer Sarah K. Byrne recently wrote and filmed a detailed tutorial on how to make multiple exposure photographs using a Cannon Mark III camera and accompanied the article with some great examples of her own work.
Self portrait ideas Mapping 2013 on Behance Use a process like this for "identity/self-concept" activity about skin color/shade/tone/palette. Put vertical photo strip of every child together on a couple images to make a collective face.