when holding an internet 'picture' contest, steps must be taken to ensure that the picture submitted wasn't taken weeks in advance. so, a specific pose...or a certain item is held in the picture that was designated by the contest organizer to ensure all pictures submitted were taken during the designated time frame.
the options are endless...i've seen a certain card from a deck, a bullet held upside down between the thumb and pointer finger, the front page of a local newspaper, certain # of fingers displayed from a certain hand...etc.