Custom Icons for my folders

it seems silly to have to post this on here cause im sure its an easy thing to do BUT

months ago i was customizing my desktop icons for music, games, and downloads

basically (for my music) its the itunes icon with a folder background, so the itunes logo fits perfectly in the middle.

well now i cant remember how i did it and i want to make one for pictures, and i googled it but not sure how to word the search query....so basically i was wondering if someone could remind me how i did this

thanks in advance