Image analysis – Applications
Reexamination Certificate
1996-02-09
2001-03-13
Couso, Jose L. (Department: 2721)
Image analysis
Applications
Reexamination Certificate
active
06201879
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to steganography. More particularly, this invention relates to techniques for embedding inconspicuous and readily recoverable figures in still images.
BACKGROUND OF THE INVENTION
A well-known, time-honored method of incorporating creatorship information into a work of art is the application of a signature to the work itself. In the case of a two-dimensional image, such as a photograph, the signature typically obliterates the information it overlies, and is therefore applied to a peripheral portion of the image. Although the signature has the desirable attribute of ready availability to anyone possessing the image, it may interfere with proper use of the image or be otherwise distracting or annoying to the viewer. This problem also persists in the realm of digitally represented data, in which it would be desirable, for example, to mark photographs or other types of images as proprietary material before electronic publication or distribution through on-line services, or to vary the signatures marking different versions in order to identify different routes of distribution.
Data hiding is a class of processes used to embed recoverable (e.g., signature) data in digitally represented information, such as a host image, with minimal degradation to the host information. Although the changes introduced by embedded data may be perceptible by a human observer, they need not be conspicuous. The goal of data hiding is not to restrict access to the host information, but rather to add the signature information to the host so that they can be distributed together. The ability to embed inconspicuous data makes data hiding attractive for adding signature information to digital and analog images.
Several known low-bit data hiding techniques afford encoding of information in a minimally perceptible fashion. Typically, however, recovery of the embedded data requires recreating specific details of the embedding process. Although this restriction makes the encoded information highly resistant to unauthorized removal, this resistance is generally purchased at the price of excluding the typical consumer of the image from accessing the encoded ownership or copyright information.
DESCRIPTION OF THE INVENTION
SUMMARY OF THE INVENTION
The invention exploits the relative insensitivity of the human visual system to discontinuities over a region of random texture to hide a figure, such as a logo, in the texture patterns of a still image. Specifically, the figure is encoded in an original image by altering the image in the following manner: copying an area having the shape of the figure to be embedded from one location of a texture field having a significant random or high-frequency component in the original image to a second nonoverlapping location in a similarly textured region of the same image. Several such figures can be encoded in a single image provided that it contains a sufficiently large area of appropriate textures.
Decoding the figure first requires locating the identically textured regions in the modified image. Correlating the image with a copy of itself is a convenient and well-known analytical technique enabling location of the copied information. The results of this autocorrelation indicate the relative placement of the modified image with respect to its copy that will align the identical regions. After positioning the modified image and the copy so as to align the repeated pattern segment in the copy with the original location of the pattern segment in the image, the copy is subtracted from the image. The resulting pixel brightness values at locations within the embedded figure have absolute values near zero, so that the dark shape of the figure is revealed. The outline of the figure against its surroundings is sharpened by resetting the brightness values falling under some threshold magnitude to black and the values greater than the threshold to white.
Since the source and target regions are identical, they are modified in the same way by any uniform transformation of the image. If the two regions are reasonably large, the inner part of the copied portion changes identically under most non-geometric transformations. Coded regions as small as 16×16 pixels have been found to be recoverable after the modified image is subjected to filtering, compression, and rotation.
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Bender Walter
Gruhl Daniel
Morimoto Norishige
Couso Jose L.
Massachusetts Institute of Technology
Testa Hurwitz & Thibeault LLP
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