I found this make-it-yourself artwork at Ohcrafts.net who found it from the original source at anestforallseasons.blogspot.com. The creator painted her baby's feet with white paint and very carefully printed the footprints onto a painted board. Doing this every few months shows very sweetly how the little tyke's feet grow.
Such a great yet simple idea! I wish I had thought of this for each of my kiddies, but at least I have a lovely idea for the future grandkids!