wm_koch_d(1)

NAME
wm_koch_d - a program to extract signature bits that have been embedded into the DCT coefficients of an image

SYNOPSIS
wm_koch_d [ -h ] [ -o ofile ] [ -q number ] [ -v number ] -s sfile file

DESCRIPTION
wm_koch_d is a program to extract signature bits from the 8x8 DCT coefficients of an image, embedded with the wm_koch_e watermarking program. cmp_koch_sig program compares and tests the extracted signature against the original signature.

The input image is in PGM (portable graymap) format.

If file or ofile is not specified, then standard input or standard output is used. The signature sfile is a mandatory parameter however.

Please refer to E. Koch's paper "Towards Robust and Hidden Image Copyright", 1995, to get an idea about the algorithm.

OPTIONS

-h  Print a help message.

-o ofile
    Output the extracted signature to ofile instead of standard output.

-q number
    Quality/robustness factor used to extract the signature. Overrides setting from signature file.

-s sfile
    The original signature file. See gen_koch_sig (1) for a description of the file format. Mandatory parameter. -v number Verbosity level. 0 for quiet operation, higher numbers for more output. Default value: 0.

file
    Signed (watermarked) input image in PGM format. Default: standard input.

OUTPUT
The extracted signature is written to standard output or, optionally, to ofile.

The extraction algorithm examines the relationship between two random coefficients of randomly selected 8x8 DCT blocks to reconstruct the signature bits.

The output file has the following format:

KCSG
    Magic to identify file type.

number
    The length of the signature in bits.

number
    The quality/robustness factor.

number
    The seed value for the pseudo-random number generator.

string
    The actual signature bytes.

AUTHOR
Peter Meerwald. Email bug reports to pmeerw@cosy.sbg.ac.at.

AVAILABILITY
The most recent released version of wm_koch_d is always available at http://www.cosy.sbg.ac.at/~pmeerw/Watermarking or via anonymous ftp from ftp.cosy.sbg.ac.at in the directory /pub/people/pmeerw/Watermarking.

SEE ALSO
gen_koch_sig (1), wm_koch_e (1), cmp_koch_sig (1)