How do you make a single picture made up of a photo collage of different picture

Question:

How do you make a single picture made up of a photo collage of different pictures?

Hi guys. I've been searching all over the internet, what do you call this art? Let me explain more clearly. I've seen this so many tiems yet I dont know what it's called. I'm pretty sure it's computer generated.

A photo (for example Brad pitt's face picture), and this photo is made up of tiny pictures of let's say him and angelina, him and jennifer, a picture of their house etc.. yet all those pictures when combined looks like his face?

SOO HARD TO EXPLAIN!??!?!?!? IF ANYONE GETS WHAT I'M SAYING GOOOOD!

what do you call this and how do you make this?

Additional Details

1 week ago
here is an example... only difference is my question is how do you make something like this with tiny PICTURES not just blocks of color

http://www.portrait.gov.au/exhibit/heads...

Best Answer - Chosen by Asker: 1 week ago
here is an example... only difference is my question is how do you make something like this with tiny PICTURES not just blocks of color

http://www.portrait.gov.au/exhibit/heads...