After some experimentation...

I have been fooling around with various means of doing external image resources.  Basically I think that, for the most part, the viewers do not support it very well.  Pasting the same IOCA image data into the page directly works just fine in most AFP viewers.

I an still waiting on some technical support for a couple of the viewers to see if that clears things up.

I also started working on how well AFP works when stitching together parts of an image.

For this I broke a larger image into parts and set up some AFP pages to stitch them.  To do this I set the resolution of the page and image to be the same, in this case 600 dpi, and then placed the images next to each other.  This seems to work well in all the various viewers.

It is my as yet unproven belief that AFP, unlike PDF, allows devices specific pixel alignment and placement.  PDF is, as you may or may not know, totally device independent in that regard and, further, you are not allowed to "know" in the PDF code about the device resolution.  PDF images have a specific resolution at which they are defined but they are always transformed via a CTM prior to display.  Since CTMs are based on floating point numbers there is no guarantee that things will line up evenly on the display device.

AFP seems very focused on specific image and device resolutions.  So far I have no reason to believe that it does not allow stitching of images and so forth at the device pixel level.  There is no CTM-style scaling for IOCA images so I don't expect much problem.

A note on the viewers.

There are two main types - browser plug-ins and stand-alone applications.  Both IBM and ISIS offer browser-based viewers.  I have been using both for the last several days.  IBM also offers a stand-alone application.

The ISIS viewer offers the most impressive display capabilities so far.  I really like its anti-aliasing capabilities for display and its fast, smooth scrolling and scaling.

The IBM viewer is very tolerant of errant AFP and supports external resources as you would expect.  IBM set up a joint venture called InfoPrint with its printer division and Ricoh in 2007.  So far all of the AFP support still appears to be on the IBM site.

I guess the real question is how all of this will print.  So far I have not worried too much about that but that will no doubt be a source of misery very soon.