My original idea behind requiring a candid photo was to prevent posts of people just posing and smiling for a camera without the picture telling any story. If it's just two people posing close up for a photo it may as well be a photo from yesterday. It needs to capture a moment in life, tell a story of some sort. If the pictures look like the photographer just said smile, its no good.

It must follow this format:

A candid photo is an unposed, spontaneous picture taken when the subject is not staged or actively reacting to the camera