Yes, it seems FastView is the only option for a basic A500 setup: I thought about Visage, but it needs ECS and OS 3.0 at least (I think you probably have KS 1.2/1.3 or 2.04).
Cheers!
P.S. If JPEG images are not 4000x3000 it's not such a big hassle to wait for few seconds for the image to be displayed.
...a bit of patience (I remember...).
