The article is original or translated by Haohappy.
JPGraph is now one of the standard choices for PHP image processing. I have wanted to write a related article for a long time, but I have never done it :(
http://www.aditus.nu/jpgraph/index.php
GraPHPite is also a good choice. It is open source, free, OO, and easy to customize and expand.
http://graphpite.sourceforge.net/