There's two files in his example - the main PHP that does the work and a font file to pull the text from. The code is pretty straight-forward, and can almost be cut and paste into any kind of application. Working with the font file is a little tricky, but GD has built-in functionality to work with it.
The script allows for any kind of true-type font input, multiple color schemes, transparency, and the ability to angle the letters to make them harder to interpret. The resulting output from his script is a PNG image, but with a few modifications, it could create JPEGs as well.