C code is too "random" to produce nice images. You can use the least significant bits to hold some data; Google "steganography" (this is just the most basic).
In a world where it is possible to compute a file that contains its own MD5, I wouldn't bet on this. Wish I could find the link, there was some feted programmer who had a friend that bet him such a thing was not possible. He proceeded to write an algorithm that found such a file by brute force.
I wouldn't count on the eventual C being pretty though.
Ultimately it's never going to be pretty if it's human readable as the range of bytes used will make a lot of greyish tones.
C/C++ wouldn't look a lot different I doubt, but if you want you can grab my python script (PIL required) and pack some source files and see for yourself:
In Java, source files can contain unicode escapes[1] of the form '\uXXXX' which are expanded prior to tokenization. In effect this gives you several options for what characters can exist in a given "pixel". I think that this, combined with careful application of whitespace and comments, should easily provide enough flexibility to make arbitrary code look roughly like a desired bitmap.
