Now you can get infected, just by visiting a website or opening a mail that has a picture in it. This has to do with a problem in the way windows renders certain image files (.wmf or Windows Meta files). Sunbelt Blog has posted about a vulneribility (weakness) in all versions of Internet Explorer and some older versions of Firefox (see F-secure post). One more reason to switch to (the latest version of Firefox?)
Update:
This seems to have caused quite a noise on Slashdot. F-Secure weblog points to an advisory on the Microsoft site to temporarily (repeat temporarily!) circumvent this problem.