like a picture already has i white back ground and you wanna get rid of it to use in a sig or banner....
Ah, well most renders dont have the white background when saved as a .PNG. But for other pictures you could just select the white area with the magic wand tool with a low tolerance. Or use a magic eraser tool.
Yeah, when you select the magic wand tool, you can set the tolerance at the top. The lower the tolerance, the more specific color it selects. Somewhere around 10 is good :3