Tobias Schlitt has posted about a script that Jakob has created to make class graphs from the existing PHP source in a directory.

The resulting SVG is generated through GraphViz. He just ran the script on the eZ components.

It's a bash script that can run local to the machine and make the images as it speeds through your PHP code. Jakob mentions that the script it free for all, and offers a direct download from his page. You can see a more full-size example in the current graphs of the eZ components trunk.