There is an app called photo Tlock on the app store. Seems it was designed for self-bondage or chastity players. Like some of the online sites like Emlalock it stores a picture for a pre-determined length of time. You can take a picture from the app and store it, it will not release it until the time is up. It requires an Internet connection for the time base, so no cheating there.
It has a pass code for safety if you like.
Times are from one minute up to one year.
It is expensive as far as aps go ($9.99), but it does a good job. I am not affiliated with the author or company, just my review of the program.