What you needClear marbles (the ones with one flat side, can be found at any craft store)
Old magazines or stickers
Clear Silicone or PVA (white)craft glue or modge podge.
Cut a piece of cardboard or paper backing the size of your marble. Then glue your image onto the cardboard.
Then glue the marble to the top side of the picture so that you can still see the picture. Let it dry.
When the glue dries you will be able to see the picture through the marble.
Finally, glue magnets onto the back.