I often get this whenever the item being scanned is white and glossy(photo/plastic covered)I never did sort out howto reduce it on photos without ruining the pic,but plastic covered often putting a plain white piece of paper behind the object cured it.
If you go in to the properties of some scanner programs (and Graphic programs), you will find that you can alter the Gamma value which is often set at 1.0 as default. By increasing this value to approx 2.0 (bit of trial and error here) you can lighten the picture and make the background white instead of bluish. This is also one way in which I have balanced the scanner output with the monitor and printer. If it doesn't work then simply reverse the value back to the original figure.
This thread is now locked and can not be replied to.