FIELD: information technology.
SUBSTANCE: method comprises a step for inserting a secret digital message in which an initial image for printing is rasterised, regions are detected in the component black colour of the rasterised image which are suitable for inserting information marks, exact positions for inserting the information marks are calculated, the volume of information which can be inserted into said image is calculated, the message is inserted into the composite black colour of the rasterised image, the rasterised image is printed, and a step for extracting the secret image, where the printed document is scanned and the scanned image is stored in memory, contrast of the scanned image is enhanced, a binary image is obtained from the scanned image via threshold processing, the binary image is filtered, regions are determined on the binary image in which the inserted marks are hypothetically located, contrast of small light spots on a dark background within regions determined at the previous step on the scanned image is increased, the position of the inserted marks is detected and the inserted marks are identified, and the structure of the extracted message is reconstructed.
EFFECT: high degree of protection of documents from copying owing to insertion of a secret unique digital message into the document.
10 cl, 10 dwg
