Seeing right through it
When scanning text or images from a published source, the material on the back of the page can show through and be difficult to eliminate. This is not helped by the fact that most flat-bed scanners have a white surface under their lid. Place a black sheet (print your own if necessary) face down on the back of the page to be scanned. This will swallow the unwanted ‘show-through’ into a uniform grey background in the output, which is easily corrected out using the brightness and contrast controls in the scanning software or an image editor such as the excellent and free Gimp. This works best when the offending material is black or grayscale, of course, but it will at least improve things with colour material.