To add a photo, you simply have to search for one on your hard drive of a person looking straight on, never turned to the side, and How Old Do I Look? starts calculating the age that the person appears to be. The tool also allows for photos in which multiple people appear, calculating the age of everyone in the photo at the same time.
The majority of the time, the app tends to be a little off, and for that reason, there's a disclaimer message at the bottom of the page, asking for understanding and patience while they continue to improve the tool.
In any case, although How Old Do I Look? is not extremely effective, it's sure to provide a great deal of entertainment while you calculate the ages of your enemies, neighbors, and favorite characters and also enjoy the most incorrect guesses.