This web program will read the JPEG image you specify below and correct the color balance to make the whites appear whiter. The resulting image will be displayed, and you can drag and drop it to save it on your computer.
Example image before and after processing:
p.s. Since this is a pretty simple program, it might not work if two people use it at exactly the same time. Just wait a second and try again. Also, my program works for most versions of JPEG, but there are some images it will not work for. Try reading and saving these images using a standard program like MS Paint, and it should work.