Basically this is a simple URL change to make a picture that was small larger. Say you see a person who is not your friend so you dont have access to their Myspace however you can see the tiny thumbnail of the picture that you would like to see in the full size. Its just a simple change of the URL and woo la you can see it larger.

example this would be a small thumbnail size pic:
http://c4.ac-images.myspacecdn.com/images01/31/s_31c30dc4ebcab76c728ffa3aaf46e9w7.jpg
or it could look like this
http://b2.ac-images.myspacecdn.com/00000/20/52/2502_s.jpg

simply change the "s" and you can get a better look. Here is how myspace breaks down thier sizes:
Small="s"
Medium="m"
Large= "l" <--that is a lower case L not a one

so to see that picture larger you would change it to this:
http://c4.ac-images.myspacecdn.com/images01/31/l_31c30dc4ebcab76c728ffa3aaf46e9w7.jpg
or
http://b2.ac-images.myspacecdn.com/00000/20/52/2502_l.jpg

OK so your asking HOW do I get the URL for the picture. Well in Firefox simply right click on the picture and pic properties and you can see it there.

side note: the first URL I used as a example is a non working one (numbers and letters changed) but the second one was myspace "tom"