what programming language are you using? flash, javascript, html, css, java? on the client side of things. that will most likely determined what is available for you. there are lots of "chart" scripts out there for flash, javascript, css, java. to many to count.
GD graphics library, and imagemagick are server side applications in dealing with images. at one time they were pretty much standard install on nearly every server on internet via web hosting companies. ((it has been a few years since i went looking so i do not know current state of things)) with different frameworks / api's to access the apps from php, perl, cgi, c, java, etc..