Snapchat is an app that is designed so that people can send 'snaps' to each other which are shown on screen for a predetermined amount of time (set by the sender) and will then disappear.
Because many people use Snapchat to send pictures that they would think twice about sending if they thought that they would not disappear after a few seconds, this is a rather worrying thought.
My advice, therefore, is not to send photos that you are not happy to have them on the internet when you are famous!