Perl library and command-line application for reading, writing and editing meta information (EXIF, IPTC, XMP, and more) in a wide variety of file formats (JPEG, TIFF, PNG, PDF, RAW, and more).
...It is specifically designed to handle comic books (both Western comics and manga) and supports a variety of container formats (including CBR, CBZ, CB7, CBT, LHA and PDF). MComix is a fork of Comix.
J-Watermarks is an easy to use system to generate custom watermarks for images and PDF too.
Users can customize the marks colors, transparency and much more