This is what you will be making...

1) Get a picture you want to use for the new background.
2) Make the picture layer...call it BG.
3) Insert another layer named text.
4) Now...select the picture and press CTRL+B. This will break the picture.
5) Select the eye-dropper tool and click on the picture.
6) After you have done that...the fill icon should be the picture you have.
7) Delete the picture that is on the stage.
8) Select the rectangle tool and set the radius to 50.
9) Make random squares on the stage and watch your picture come back!
10) Add some text/caption for your picture. You're done!