You're running KS/WB 3.1? I tested the 3.9 version of MultiView with a JPEG from my 12MP camera and it displays fine on a 640x512x256 AGA screenmode. The Datatypes use Fast RAM to store the image. I did notice it took over 30MB of Fast RAM though.
You may want to consider more Fast RAM through something like a CPU board or a Zorro III card as large JPEGs need lots of RAM to decode. I'm not sure what programs you could try if you are running 3.1 but have a look on Aminet for either updated Datatypes (such as the picture.datatype and jpeg.datatype, I'm using WarpJPEG+OS3.9 Picture Datatype) that support loading to Fast RAM or an image viewer that supports this feature.
