1. Allison, R., Hart, J.: Paper watermarks, paper making, and dylux proofing paper. http://abacus.bates.edu/Faculty/ wmarchive/wm-initiative/index.html. Last accessed: 12th November 2006
2. Ash, N.: Recording watermarks by beta-radiography and other means. In: The Book and Paper Group Annual, vol. 1. American Institute for Conservation of Historic and Artistic Works, Washington (1982)
3. Badke, D.: Paper-based watermarks and beta-radiography method. http://gateway.uvic.ca/lydgate/lydgatems/pages/ manuscript/watermarks/wa termarks.htm. Last accessed: 12th November 2006
4. Canny J. (1986). A computational approach to edge detection. IEEE Trans. Pattern Anal. Mach. Intell. 8(6): 679–698
5. Gants, D.: Pictures for the page: techniques in watermark reproduction, enhancement and analysis (1994). http://jefferson.village.virginia.edu/gants/BibSocUVa/ paper.html. Last accessed: 12th November 2006