Abstract
Watermarking is a technique used to authenticate and distinguish original documents or images from the copied or forged ones. Many watermarking methods have been developed and are being used for printed documents and images. Though these current watermarking techniques can distinguish between original and forged documents, it is not possible to identify the source of the forged and counterfeit documents, knowledge of which is required in some cases to stop future forgeries. In this thesis we propose a machine readable watermarking technique for images, halftoned using clustered-dot halftoning technique and printed on electrophotographic printer, that can, not only identify forged documents and images, but also provide information about the printer used and date on which the document was printed.
First, we propose a method of embedding data in the image by shifting clustered-dot pair diagonally and horizontally. The range of gray level values within which data can be embedded, number of pixels by which dots should be shifted and location of shifted dots is decided based on experiments carried out.
Next, we propose a method for detecting data from the scanned image. Scanned image is preprocessed using various image processing algorithms and techniques before detection stage. The detection of embedded data is done from the knowledge of the centroids of each clustered-dot. Error control coding technique is also proposed to improve the accuracy of detection process.
Lastly we propose an embedding method using pulse width modulation to reduce the visual distortions in the image caused by embedding the data.
Keywords
Watermarking, Machine readable, Clustered-dot halftoning, EP printers
Date of this Version
April 2008
Department
ECE
Month of Graduation
May
Year of Graduation
2008
Degree
Master of Science in Electrical and Computer Engineering
Head of Graduate Program
Prof. MJT Smith
Advisor 1 or Chair of Committee
Prof. Jan P. Allebach
Committee Member 1
Prof. Jan P. Allebach
Committee Member 2
Prof. Edward J. Delp
Committee Member 3
Prof. George T. Chiu