In this paper we propose an image watermarking algorithm based on constraints in
the Discrete Cosine Transform (DCT) domain. An image watermarking algorithm has
two stages: signature casting (embedding) and signature detection. In the first
stage it embeds an identifying label in the image. This is recognized in the
second stage. The proposed algorithm has two processing steps. In the first step
certain pixel blocks are selected using a set of parameters while in the second
step a DCT coefficient constraint is embedded in the selected blocks. Two
different constraint rules are suggested for the parametric modification of the
DCT frequency coefficients. The first one embeds a linear constraint among
certain selected DCT coefficients and the second defines circular detection
regions according to the given parameters. The watermarks cast by the proposed
algorithm are resistant to JPEG compression and filtering.
© 1998 Optical Society of America
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