Printed images may soon contain hidden data that mobile phones can see and respond to. A telephone number embedded in a CD cover picture will be able to be dialled. And a poster image containing a URL invisible to the human eye will be seen by a PDA camera and the website displayed on its screen.

Fujitsu Labs has invented a new technology to embed data in printed images. This procedure, commonly called steganography, meaning hidden writing, is used to watermark digital images as a way of identifying them and detecting piracy. Such watermarking usually damages the image quality. But Fujitsu labs claims to have perfected a way of preserving image quality while adding the data. Numeric characters of up to 12 digits, such as a telephone number or numeric conversion of a URL address can be embedded in a 1cm x 1cm section of an image.

It takes Fujitsu?s PDA 0.4 seconds to detect and decode the data, and Tsugio Noda, a research fellow in Fujitsu Laboratories, said an ordinary mobile device would take one second.

The original image and the data to be embedded are combined into one set of code, a TIFF or JPEG image for example, which is then printed as one picture. The way the combining is done is to divide the original image into smaller blocks of 0.8mm square or less. The average gradation or density level of each block is analysed and then the information is added as a sequence of yellow dots which have a lower gradation.

Human eyes cannot see this particularly way of treating yellow dots in such a small space. So the data is imperceptible to our eyes but can be seen by a digital camera with optical character recognition (OCR) code that detects the yellow dots. Fujitsu reckons that the code can be added to mobile phones or PDAs with digital cameras. A demonstration of a similar process was shown at Intel?s Developer Forum in 2003 using an Intel mobile phone platform to detect an image?s digital watermark.

Such steganographic burying of data means that the image doesn?t need the information visibly printed on the page and taking up space. In Japan, one or two dimensional barcode technology is often used to contain telephone, URL and similar data. Such barcodes look ugly and could be dispensed with using the Fujitsu technology, the company claims. Consumers could even embed information in pictures printed on their inkjet printers.

Applications include automatic mobile phone dialling to, for example, get a ring tone download from a music CD?s cover image data. Information about a shop or restaurant could be collected while reading about them in a magazine for example a GPS location. Printed card-based games can also be envisaged.

The technology is open to abuse though. Secret data, such as passwords, could be embedded in an image and openly taken out of secured premises. Soft porn or porn images could have adult website URLs secretly added to them or, worse, premium rate telephone lines could be activated.

Fujitsu Labs may talk to mobile phone and PDA manufacturers about productising the technology.