In this DevX tutorial, Octavia Anghel shows how use PHP to create images based on the SVG libraries available to any browser.

Scalable Vector Graphics (SVG) is an XML specification for producing vector-based graphic content that you can create, modify, and manipulate dynamically from programming languages. Here, you'll explore the most important techniques and libraries for integrating SVG with PHP to create diverse graphic content—from simple shapes to complex graphs.

They show a few different ways to get the job done including a straight 'echo' call with the output, sending a converted SVG document over with a PHP header or including another (or multiple) SVG documents into another and outputting them. They also talk about tools like the phpHtmlLib library, the PEAR::XML_SVG package and the PEAR::Image_Canvas package.