Preventing from black background when resizing/cropping JPG images with Image_lib

[eluser]luismartin[/eluser]
I've googled this issue and all I've found are solutions for transparent PNG's whose transparent pixels were converted to black when resized, but nothing regarding JPG's.

When I resize big images (most of them have light grey colors, so I'd like the background in cropped images to be white) they are framed with an ugly black background.

Is there an easy way to use white instead?