Abstract: A method of embedding watermark data in a two-color image includes assessing the suitability of each of several candidate pixels to embed a bit of watermark data. Candidate pixels for which one pixel directly above, directly below, and immediately to the left and right of the candidate pixel have different colors, are identified. In one embodiment, only a single candidate pixel in each 2×2 block is identified. Suitability of each candidate pixel may be determined based on a relationship of coefficients computed from a binary wavelet or binary lifting transform formed from the image. Data is embedded by inverting suitable pixels. A recipient of the image may assess which blocks contain watermark data, by assessing the suitability of each 2×2 block in the image to embed data and extract data without further information about the data's location.

Abstract: A method of embedding watermark data into a two-colour (binary) image includes dividing the image into blocks and assessing the suitability of each block to embed a bit of watermark data by assessing whether or not the flipping of a defined pixel in each block affects the visual attributes of said block in manner to be perceptible by the human eye. Data is only embedded in those blocks determined to be suitable for data embedding, by flipping the defined pixel, as required. A recipient of the document may similarly assess which blocks contain watermark data, by assessing the suitability of each block in the document to embed such data. Conveniently, watermark data may be extracted without further information about the data's location within a document.

Abstract: A method of embedding watermark data into a two-color (binary) image includes assessing the suitability of each of several candidate pixels to embed a bit of watermark data. This is done by identifying candidate pixels for which one pixel directly above the candidate pixel and one pixel directly below the candidate pixel have different colors; and one pixel immediately to the left of the candidate pixel and one pixel immediately to the right of the candidate pixel have different colors. In one embodiment, only a single candidate pixel in each 2×2 block is identified as flippable. The “flippability” of each candidate pixel may be determined based on a relationship of coefficients computed from a binary wavelet transform or binary lifting transform formed from the image. Data may be embedded by inverting selected candidate pixels. A recipient of the document may similarly assess which block contain the watermark data, by assessing the suitability of each 2×2 block in the document to embed such data.