In this appendix, we provide most of our source code for the example watermarking systems tested in the book. This code is intended to help clarify the descriptions of those algorithms, and to show every detail of our implementations that might affect the test results. Toward this end, we have attempted to make it match the descriptions of the algorithms as closely as possible, often at the expense of efficiency. We have also attempted to avoid some of the more cryptic constructs in the C language, such as the "+=" operator and pointer arithmetic.

The source code for each watermarking system is presented in its own section. The source for any routine called by more than one system is given only in the section for the first system that uses it. In subsequent systems, we indicate where the routine can be found.

In a few cases, we do not present source for routines that implement standard algorithms, such as computation of 8 8 DCTs. Instead, we provide a comment block describing the routine's calling conventions, followed by a note indicating the algorithm used.

Throughout the following source code, images are represented with arrays of 8-bit integers (unsigned char in C), with 0 representing black and 255 representing white.