Print the picture.
Cut out the picture. Do not cut out the pieces... just the main picture.
Cut out one large side of the cereal box.
Put a nice coating of rubber cement on the back of the picture and press onto the cereal box (picture side of box so that the cardboard is showing).
Let this set up... until the picture is dried to the cardboard cereal box. You don't want the picture to scoot around on you. Cut out the rectangle jigsaw puzzle.
Carefully use your scissors to cut out the jigsaw pieces. Use the jigsaw puzzle lines as your guide and cut out the pieces.
When you are done with the puzzle, store the pieces in an envelope.