ORDINARY office printers could create documents with a “watermark” that cannot be photocopied. Its inventors say the technique will make counterfeiting more difficult, but others argue that its very simplicity makes it of little use in fighting forgery.
Researchers at the Xerox Laboratories in Webster, New York, made the discovery while studying why images made by laser printers sometimes show glossy patches. These images are made up of dots of four different colours arranged in a regular structure, known as a half-tone grid. Each dot is a blob of polymer toner that catches the light at a specific angle, like…
