"Ultrasound pictures" refer to images produced through the use of ultrasound technology, which uses sound waves to create pictures of the inside of a person's body. Full definition
Doing special things to remember your baby may help, like gathering and keeping mementos in a scrapbook such as ultrasound pictures (if you received some), sympathy cards or pressed flowers that people gave you and poems or letters you wrote to your baby. (pregnancy-baby.com)