I'm trying to identify the basic biological mechanisms for sight.    
  
Could you help me with identifying any organism that has the most basic ability to see objects?    
  
Most importantly, creatures like dogs, cats, insects are able to not just see light, but are also able to identify objects and other living beings. I feel that an organism could be classified as "being able to see" if it can identify objects and movement and use its "visual sensory organ" to help it move around, locate food, identify species of animals, differentiate between living and non-living and escape predators if any.  
  
Even if an organism can see just black and white or the most basic perception of sight, it would qualify for what I'm searching for. Is there any such known organism that has such a basic visual perception and has the way its eye+brain perceives images, been studied?  
  
I'm not referring to the kind of "photosensitivity" that plants have. Detecting the presence and direction of light is not sufficient.