Images are printed on paper as many dots of ink. These dots, sometimes visible to the naked eye, become obvious in unprocessed scans if the scanning resolution (usually 600 dots per inch) is higher than the printed resolution (often 300 DPI). Things printed in very high resolution, such as paper money, do not have this problem. Resizing an image down does not help much, since it creates an ugly moiré pattern. It is usually not a good idea to use the built-in descreening option on your scanner.

For more information on how to remove screening from scans, see:
http://moe.imouto.org/forum/show/2007
http://moe.imouto.org/forum/show/2290

Updated by Aurelia over 15 years ago