More and more people are turning to the Internet as a means of transmitting and displaying images.
Due to the ease with which those images can be downloaded, copied and re-distributed, there is a growing demand for methods to protect image copyrights.
The various methods of digital watermarking, fingerprinting, and signatures can be used to discourage unauthorized use of images.
Watermarks can be invisible or visible, depending upon the function they are meant to serve.
Title: Watermarking Digital Images for Copyright Protection
Citation: Proceedings of the 5th International Conference on Image Processing and its Application. Edinburgh, UK. IEE Publication No. 410. pp. 326-330. 4-6 July, 1995.
Description: Boland FM, et al, describe variations of the invisible watermarking process, including methods of placing the marks, and how to choose a reliable and secure system of transmitting the mark. The results of embedding marks into images identify both the source and recipient of those images. The images are not visibly degraded by the marks, the marks are recoverable by comparison with the original, the marks are highly resistant to decoding and they can survive image compression.
Title: Protecting Publicaly-available Images with a Visible Image Watermark.
Citation: Proceedings of the SPIE - The International Society for Optical Engineering. Optical Security and Counterfeit Deterrence Techniques. Vol. 2659. pp. 126-133. 1-2 February, 1996.
Description: The authors describe their efforts in the Vatican Library Project and the Luther Library Project, where they used visual watermarks to discourage unapproved publication.
The method includes altering the brightness of pixels. In order to make the watermark more resistant to attempts to remove it, the brightness of the unique pixels is randomly assigned and the watermark is placed in the area of the image with the greatest detail. The location of the watermark on images also varies randomly, to thwart global editing of the watermarks.
Title: Digital Watermarking
Citation: Proceedings of the SPIE - The International Society for Optical Engineering. Optical Security and Counterfeit Deterrence Techniques. Vol. 2659. pp. 99-110. 1-2 February, 1996.
Description: This process to mark digital images with invisible information uses keys held by both sender and receiver to identify the watermark in the image. The keys are hidden by using frequency modulation of their binary image.
Title: A Digital Watermark
Citation: Proceedings of the 1994 1st IEEE International Conference on Image Processing. Part 2 (of 3). Austin, TX. pp. 86-90. 19941113-19941116. 94CH35708.
Description: Invisible watermarks are able to carry authentication codes and legends for interpretation of the image. Two methods of incorporating the watermark into the image offer opposite benefits of security and rapid decoding.
Title: Marking Text Features of Document Images to Deter Illicit Dissemination.
Citation: Proceedings of the 12th IAPR International Conference on Pattern Recognition. Vol. II Conference B: Pattern Recognition and Neural Networks. pp. 315-319. October 9-13, 1994.
Description: Line-shift coding (vertically shifting the locations of text lines), word-shift coding (shifting words horizontally within text lines) and character coding (coding the bitmap image of a document) are discussed as possible coding mechanisms. The line-shift mechanism appears the most reliable for detecting watermarks and the most resistant to degradation due to copying.
Related information can be found at:
Luther Library Book Cover Image Sixteenth century book cover plate watermark based on the Luther Rose.
Behind the Scenes Look at the Vatican Library Project A press release from the IBM Corporation. Feb. 27, 1995
IBM Cultural application: Example images, including the Vatican Library, the Klau Library of Hebrew Union College-Jewish Institute of Religion and Lutherhalle Wittenberg Museum.
Companies that offer software and services to support watermarks and otherwise encrypted images: