Figure-Ground Perception

A type of perceptual grouping which is a vital necessity for recognizing objects through vision. You see the foreground of an image and everything else that forms around it is just the background. 

At first you just see pillars, and then with a closer look, you see the people in it

Proximity

Objects near each other are grouped together.

In this picture the girls are grouped together and the boys are grouped together because of their proximity to one another.

Similarity

Items that are similar tend to be grouped together by our mind.

In this picture, you'll view vertical columns of colors(because they are similar) rather than horizontal columns.

Continuity

We like perceive fluid and continuous figures rather than disconnected ones.

You'll see this as a smooth path of dominoes, rather than seeing different lines and angles.

Closure

Rule of perceptual that states that we tend to fill in the blanks and missing pieces and see things as complete
.
In this picture, you'll see a triangle even though it is just cut up kiwi.