Don't forget how large a full screen's picture is in comparison to the size of the diskette the OS came on! You'll need to provide your own picture. Also don't forget that the picture will be shown in as many pictures as your Workbench is, so if you're running without a graphics card, you'll have to choose your picture carefully.
One other thing, make sure it's in a format that is supported. I can't remember for sure but I think you need a datatype installed for JPEGs and things, whereas an IFF (ILBM) should display anyway. If you want to display a JPEG, check akJFIF datatypes on aminet (
http://aminet.net/package/util/dtype/akJFIF-dt).
