Cut the background from your photos. Using the photo as a stencil, score lines in can-sheet-metal. [Accuracy isn't important, since you can trim it later.] Cut out the metal at those lines. Tape the photo to the metal.
If the figures in your photo are standing at different distances from the camera, then you can make multiple cutouts from your photo and position them at different depths on the can-sheet-metal platform for a truly interesting effect, like a diorama.
Make them come alive. For example, have one person "sneak up" on another. Or re-enact the famous "I'm-holding-up-the-leaning-Tower-of-Piza shot." Or this meme:
You can also use the can lid as a frame and staple a bent rectangle of can-sheet to it to make a platform. As an alternative to a staple, you can score a slot in the can-sheet into which you insert the bent tab. As an alternative to can-sheet, you can build the stand from stiff paper or cardboard or hanger-wire or aluminum foil.
To make the tetrahedron photo frame, see scaffolding.
