Don't mean to dig up an old thread, but I am curious about this as well. I got mamehooker displaying instruction cards on a 2nd monitor and would be interested in having the monitor display a default image if a game doesn't have an associated image. If it can't be done, I guess an idea is to make hundreds of PNG files that are the default image making them a placeholder for the missing images, but thought I would check and see if support for this is built in to MameHooker.
Awesome set of programs Howard. Thanks for sharing..