squares on image

Does anybody knoe how to achieve the technique of square on a image? as shown in http://www.jessett.com/

Any related input would be appreciated.
Thanks in advance.

you can either make a grid pattern and then fill in random squares.

or you could make a layer with some colors over your image and go filter > pixelate > mosaic and adjust the cell size on the filter then fill in some random squares with whatever color you like by using the magic wand tool.

I would do all that stuff on seperate layers...One for the grid....Various layers for the squares w/ fills and strokes at varying colors or opacity's...Not hard to do...Just takes a liittle time and discretion...feel free to ask specifics if you don't understand