Cardboard puzzle pieces
1-inch flat foam brush
Arrange the puzzle pieces in a peace sign shape on the cardboard, then affix them with tacky glue. Let the glue dry, then trim the extra cardboard.
Slip a sheet of waxed paper into the shirt to prevent bleed-through. Use the foam brush to dab a generous coating of fabric paint onto the puzzle pieces (avoid getting paint on the cardboard as it may transfer to the shirt).
Press the stamp firmly onto the shirt. Remove it and allow the paint to dry.