paste image without background PIL

I am trying to paste man开发者_JS百科y small grayscale images into a bigger one. All images are jpegs. The small images had been previously rotated, so they have black background. What I wanted to do is to paste them without a background color, in other words, I need the background color to be transparent.

Thank you for your suggestions,

to my knowledge, jpg does not support transparency, you probably want your output to be a png, and you will need to set the alpha channel to be nothing

http://www.talkgraphics.com/showthread.php?22385-How-do-I-make-jpeg-image-background-transparent