CVS assumes that all files are plain text files. As each file is committed, keywords are expanded and newlines are converted.
This can be a bad thing if the file is in fact a binary format!
You can restrict the filename extensions to be expanded in cvswrappers. Example:
*.gif -k 'b' *.jpg -k 'b' *.pdf -k 'b'
Can also be used to specify how to merge or copy a file, or to apply a filter to a file type.