Topic awaiting preservation: .htaccess - send default .jpg if requested .jpg isn't found?

Greets!

I have a directory with thousands of .jpg files in it. I'm using an AJAX application to grab XML data from the server to display the records.

What I need is an option to display a default .jpg if the request image isn't found on the server.

Normally, I would use PHP to just do a check, but the XML can sometimes be sending out a single page with more than 100 records on it, and I don't want to bog down the server with doing all of the file checks.

Does anyone know how to do this in .htaccess? I tried using an errorDocument declaration, but that doesn't seem to work.

Guess an ErrorHandler to a php script that then outputs the default jpg (with the appropriate headers) should work?