I cannot reproduce this on Fedora 13.

* I downloaded an image 2118 pixels wide -- http://upload.wikimedia.org/wikipedia/commons/5/50/Rue-de-paris-film102jpg.jpg

* renamed the image to "tower.jpg" and placed it in the en-US/images directory of a book

* placed the following in the XML of the book:
<mediaobject>
<imageobject>
<imagedata fileref="images/tower.jpg" format="JPG"/>
</imageobject>
<textobject>
<phrase>The Eiffel Tower</phrase>
</textobject>
</mediaobject>

* set the following in the publican.cfg file:
max_image_width: 3000

* built the book. 

The image was in the book at apparently full size (I confess I didn't actually measure it, but it wouldn't fit on a monitor 1920 wide without scrolling sideways)

I then set:
max_image_width: 1000

The image seemed to be scaled appropriately.

Could you please include the XML that you used and the line from your publican.cfg file?

Created attachment 430484 [details]
publican.cfg

Created attachment 430486 [details]
xml file

This is happening on every file in the book, naturally. I just uploaded the one; the svn repo is http://svn.devel.redhat.com/cgi-bin/viewvc.cgi/ecs/JON/2.4/Basic_Admin_Guide/en-US/, if you want the whole thing.

Created attachment 430487 [details]
HTML with the sizing at 444px

If it helps, I'm on RHEL 5.4 and the brand is JBoss (package version 1.9-0.el5).

This limit is a policy imposed by the JBoss brand.

[publican-jboss]$ grep max overrides.cfg 
max_image_width: 444

It's probably better to discuss this on the internal docs comms channels as it's not related to publican development.