Figures require extension in APT and they should not.
For example, http://ehcache.sourceforge.net/nameandlogo.html shows a broken image. The APT for this page is:
Now, if I change it to [images/ehcache_logo.gif] it works. However this breaks aptconvert. The reason is that it is illegal in APT to specify the figure extension. I use aptconvert to create a pdf and single HTML page.