Roumen Kountchev of the Technical University of Sofia, working with Vladimir Todorov and Roumiana Kountcheva of T&K Engineering Co. in Sofia, Bulgaria have developed a new method for the efficient archiving and content protection of scanned documents that makes the text searchable and adds a watermark to images for copy protection and validation.
The technology takes the raw image of a scanned document and processes the text and images in the document in two different ways. The images are compressed using an algorithm known as IDP (inverse difference pyramid) that allows optical character recognition (OCR) to be carried out.
The IDP algorithm has the advantage of allowing the addition to the whole document of an extra embedded and invisible layer that contains a digital watermark. The watermark is password protected and can only be seen or removed by verified users, thus providing legal providence for an authenticated scanned document.
The team points out that the watermark layer does not interfere with the scanned image or the text, whether legal document, fingerprint, or photograph. However, if someone attempts to change the image, the invisible watermark will also be affected. Damage to the watermark will thus prove unauthorised editing of the document.