When you download the app, you can either choose to have your photo taken or you can upload from you camera roll/album. However, I found out that this app won't generate your age unless you're connected to the internet.
I have tried a couple of my photos and the ages being generated and it never got my correct age. I don't know how it processes the photo so I made an experiment. I used the same photo with a different lighting/filter. The age gap of the two photo was quite shocking.
I think it did has something to do with lighting and the sharpness of the picture which shows the lines and other blemishes on the face. I have tried it with Kuya BA and Vina (my relatives) and we had a lot of fun teasing each other.