Standing Out From the Crowd
The subject must be very different from all the others in a crowd. e.g., A black swan surrounded by white ones or a single object captured with flash while the other objects are blurred.
The subject that stands out should not stand out by the use of a photo editing technique. For example in an image of a bowl of apples, it would NOT be acceptable to make all but one apple black and white whereas taking the same photo, but having one apple stand out by controlling depth of field, would be acceptable.