Supplies:

Air dry clay in various shades
2 heart shaped cookie cutters or cardboard templates
Rolling pin
Pictures
light cardboard
white glue
pinbacks
hot glue

Method

To make a marbled look, take small bits of each colored clay and ball together.
Roll ball to a 1/8" thickness.
Using cutters or templates, cut large heart shapes from the clay.
In each large heart, cut out a smaller heart.
Following manufacturer's instructions, let clay harden.
Trim photos to show through the opening. Mount photo to back of heart, cover with the cardboard.
Trim cardboard to cover the back of the large heart.
After backing dries, hot glue a pin back onto the back of each pin.
Mount photo to back of heart, cover with the cardboard.