Print an image using a rubber stamp or a digital printer onto the center of a plain piece of white card stock. You may use colored card stock if you do not plan to paint or color in the image.
Cut the card stock to the size you want your card topper to be. Generally you would want the card stock to sit firmly centered on your card, so create the topper to be roughly 1/4 the size of your card.
Color in the image with colored pencils, paint or markers.
Using your cutout image as a sizing guide, cut a piece of foam board slightly smaller than the size of your image. You should not be able to see the foam board when it is placed underneath the image.
Glue the foam board to the back of the cut-out card stock.
Lay out the pieces of the front of your card for a dry run, moving the pieces around until you are happy with the overall look and theme of the card front. Glue the foam board to the front of the card.