nullprogram.com/blog/2007/09/08/
This is one of my projects.
The original idea for this project came
from Sean Howard’s Gameplay Mechanic’s #012. The basic
idea here is that image files are the second easiest type of data to
share on the Internet (the first being text). Sharing anything other
than images may be difficult, so why not store files within an image
as the image data? This is not steganography as the data is
not being hidden. In fact, the data is quite obvious because we are
trying to make the data as compact as possible in the image.
My “PNG Archiver” is usable but should still be considered alpha
quality software. I am adding support for different types of PNGs
(currently it does 8-bit RGB only), but I have found that using the
libpng library gives me headaches. The archiver can actually only
store a single file (just as gzip doesn’t know what a file is). This
is because I do not want to duplicate the work of real file archivers
like tar. To store multiple files, make a “png-tarball”.
The PNG Archiver stores a checksum in the image that allows it to
verify that the data was received correctly. This also allows it to
automatically scan the image for data. When it reads in a piece that
fulfills the checksum it assumes that it found the data you are
looking for. You can decorate the image with text or a border and the
archiver should still find the data as long as you didn’t disturb it.
(examples of this on the project page)