Well when you make a copy of a image, you need to paste it somewhere. Anytime you make a copy of something in Mac OS X (hold the Ctrl, click on something and select copy) its stored on what's called the "clipboard". The clipboard is nothing more then the name of a action the computer performs when something is copied. That action is to remember what is currently copied. All you have to do now is press and hold the ctrl button, click with your mouse and select "Paste". Your "copy" will be placed wherever you clicked.