Steganography, the science of burying secret messages within something innocuous, has endured bad publicity recently, with unsubstantiated rumors of missives from Osama bin Laden hidden in images on websites.

But the good guys can play, too. A new steganography-based technique hides barcodes inside pictures and could help create forgery-proof identity documents. The Concealogram, developed by a scientist from the electrical- and computer-engineering department of Israel's Ben Gurion University of the Negev, slips a two-dimensional barcode inside a halftone image, which can be read by scanning the image with a regular optical scanner. The Concealogram algorithm, created by Joseph Rosen, an associate professor whose interests are image processing, optics and holography, is "hard-copy" steganography, he says. "This is not digital steganography because the secret information is not hidden inside a digital file (such as MP3s or JPEGs), but in a hard copy print, after the data leaves the computer," Rosen said. "Also, it is not chemical steganography because the secret information is neither hidden in the material of the paper nor in the ink. The secret data is encrypted within the printed visible image in a special but simple way." The 2-D barcode is a cousin to the ubiquitous striped one-dimensional barcode. Linear barcodes hold a dozen characters that provide a reference number. The 2-D barcode, made up of a binary system of dots instead of lines, has all the information stored within so there's no need to connect to a database. A halftone image, a common way of creating pictures, is also made up of a binary set of dots. This makes a perfect match, with one able to be slipped inside the other.