JavaScript: Check if Image exists

I want to load an image into a variable, then check if that image does in fact exist, if not, I will bring in another image.

The processing goes like this: use uploads 0 to 3 jpgs via JSP/JavaBean, another user could view those jpgs, but there may not be 3 so thet will see that nasty little no-image tag in their browser. If anyone has a solution to this, many thanks.
Arthur