If you "get info" of the folder you want to change the icon for, then "copy paste" your desired image over the icon in the get info window...voila! No need to waste money on 3rd party apps that do the same thing. Also if you are feeling fancy you can make your own images with an alpha channel in photoshop, so there is a translucent appearing background, i.e. the icon does not appear to be the whole square.