I hope this is helpful. A couple of people recently have uploaded prc format books with illustrations. Unfortunately the illustrations are very small (at least on a 600x480 PDA - I guess on a low resolution device they'd be fine).

I don't know whether this is a quirk of BookDesigner (and maybe the illustrations look fine in BBeB), but there is a useful page in the mobipocket content development reference pages.

It's worth checking out the page itself, but the nub is that you can create links to 3 different versions of the image and mobipocket will pick the right one for the screen resolution of the user device. An example of the HTML to do this is:

As I say - I hope this is useful.
Thanks for the reference andym. We are always looking for ways to make our ebooks better.

The method most of us who post for both the Sony Reader and in Mobi/PRC format use is to develop the basic book in BookDesigner and then generate both LRF and PRC files from of same text. Several other older formats are also available but there is not a great demand for those formats at the moment within the MobileRead community.

After experimenting with the multiple options available in BookDesigner for PRC files, we all use the same settings to ensure a consistent product; among these settings is "Keep picture sizes." This is set to ensure that there is not automatic scaling or rotation of the images included in the source file. Is it the best for every device, no. Is it the best we can do now, yes.

vvv, the designer and programmer of BookDesigner, has updating the PRC portion of the program on his list of action items. No date has been announced for the completion of that phase.

Perhaps as more migrate to libprs500 (as some have already done) and we discover other tools for creating MobiPocket books things will get better.
It's not any better if we turn off keep picture sizes.
Anyone know of a freely available example .prc file with multiple image sizes? Baen .prc files appear to only include the ~240 pixel size. This is also the case (I think) with JB Universe and Grantville Gazette (volumes 10-13) - both of which are heavily illustrated.

A possible work around for illustrated BookDesigner generated .prc files might be to produce two versions, one with ~240x240 pixel images and the other with ~400x400 (?) pixel images. This would not be necessary for standard e-books (e.g. those with at most just a cover illustration).
You've slightly lost me. "libprs500" is a tool specifically for creating Sony Reader books. How will people migrating to that help MobiPocket books?
Doesn't seem to make any difference, Jon. The "Dr Thorndyke" books I created, for example, have full page (400x600 pixels or so) illustrations which come out really small in the MobiPocket version, regardless of whether one checks the "keep picture size" box. Try it for yourself with a large picture and you'll see what I mean.
By keeping their original files in HTML and then using some other tool to convert the HTML to mobi (very likely a tool that supports far more features).
From what Harry says it sounds like this is a BookDesigner issue.

Is the basic input for BookDesigner very different from the input for mobipocket's BookCreator? Would it be possible, at least for books with illustrations, to pass the text/source over to someone who could produce the Mobipocket version (I'm very conscious that most of the people who upload books are Sony users who produce the prc version as good citizens).
Andy, do you have the MobiPocket Creator on your computer? If you do, PM with an email address and I'll pop out an HTML of Peter rabbit from Book Designer to see what you can do with it and how easy it is.
Not yet (my Windows PC is in a box at the m,oment - long story but I'm hoping to have it up and running in the next couple of weeks). I'll PM you then. Thanks for the offer.