The system is designed to recognize humans (of different size), cars (of different shape and size), bicycles and motorcycles. The computer analyzes the objects that the camera sees and uses artificial intelligence to assign them a "value" - "this looks 80% human, that looks 92% car, etc." If an object looks less than certain % of what the computer is programmed to recognize it ignores it. It also looks for road edges and painted lanes to analyze if the object is in your path or the road will bypass it. The whole process of "recognizing" an object and deciding what to do is very fast, takes less than 200 ms.
It's a very "intelligent" system. For example, it won't slam the brakes if it sees somebody standing right in front of the car on the edge of a curve, because it is smart enough to figure out that you will turn before you hit the human. But it will react to a person that is off to one side, but walking towards the road in front of you. And it won't brake for trees along the edge of the road (because they don't look like a car or a human).
The system is NOT designed to recognize deer, dogs, cats, chicken, alligators, wild hogs, rabbits, etc. The complexity and number of different shapes that would have to be analyzed and identified as "danger" vs. "safe" is beyond what computers can do fast enough (yet). You could attempt to program the system to recognize a wide range of objects, but this would extend the reaction time, and in a system like that quick reaction time is essential.
One final consideration. Automatic braking system is designed to safe lives, not bumpers. It will attempt to brake and stop the car, but depending on your speed, road conditions, visibility, etc. it may not be enough to prevent contact. However, in most cases it will slow down the car enough to save the pedestrian's or your life. If you hit the car in front of you, it's your fault, not the autobraking system. You are still responsible for maintaining safe distance, speed and paying attention. If the autobrake doesn't avoid a collision 100% and you end up with a hefty body shop bill, be grateful to Toyota engineers for saving your a$$, instead of complaining about the autobrake system not being smart enough to make up for your driving mistakes.