Eversince I posted that photo of multiple me, a lot have been asking how I did it. To answer all the questions all at once, here are the simple steps on how to do it:
1. Set your camera and lens to manual;
2. Take a couple of shots, placing yourself at different location. Make sure that the camera settings and location remains the same on all photos;
3. Open all photos in Photoshop;
4. Choose photo that would serve as your background;
5. Drag another photo (make sure you press shift key while dragging to align two photos together) to the first photo that would serve as the background;
6. Then after dragging the second photo into the first photo, the second photo should be on another layer on top of the first photo;
7. Add layer mask on the second photo;
8. Choose brush, choose color black (if your mask is white, otherwise if mask is black), paint on the second layer on the part where yourself is located on the backgroud photo;
9. Paint slowly and you'll notice that you can slowly see your photo appearing from the background photo even if you are painting on the second layer. Finish painting until you see two of you on the photo at different locations;
10. Click ctrl-E to merge the two photos;
11. Then drag the third photo and repeat the steps (from masking to merging);
12. Repeat steps to the rest of the photos. Finish.
Hope this workflow helps...