At the end of last week, Apple rolled out a series of updates for Mac OS X 10.4. Primarily for security vulnerabilities, Apple had 15 fixes for it, including various browser bugs and privilege escalation bugs. One of them was a flaw in Safari, with the way it handled JPEGs, similar to other bugs in other browsers that could cause compromise:

A vulnerability in Safari, Apple's Web browser, could let malicious sites pose as trustworthy URLs with SSL (Secure Sockets Layer) indicators, said the alert, while in another, a specially-crafted JPEG2000 image could be used to trigger a buffer overflow to compromise the computer.
Anyone using OS X should grab the updates, especially since they are all revolving around security. Auto-updating users should already be taken care of.