Is there an easier way to get straight renders without backgrounds for sigs without having to cut out the render itself and having to use an eraser tool to erase the background around it that's left after cutting?

For example: If I had a render of some random dude standing in the woods, how can I just pull the image of the guy and nothing else? I'm assuming there's a way with either MS Paint or Photoshop 7. Please don't tell me that I've just got to cut him with as little background as possible and then zoom in and erase every little background pixel around him....