Do you remember Chatroulette? It was a web service that let pairs of webcam equipped strangers randomly connect to each other for video chats. While its original purpose was to let people have random video chats, the service was probably best known for its significant number of NSFW (not safe for work) random encounters.
The recently released Qik Video Connect for Android provides the possibility for a Chatroulette-like video encounter. So, Qik let its users know about a simple option they can turn on to prevent anonymous callers.
It is a simple matter of unselecting a single checkbox under Settings->Privacy.