The '--referer=http://www.etc.etc...' entry can be used in the Scan Options. 
But this only allows one referer to be used even when downloading from
multiple sites.  A feature in which the referer is dynamically updated is
needed.  A simple feature such as '--referer=%url%' could accomplish this,
replacing '%url%' with the URL of the site being downloaded.  The problem I'm
having with the latest version of WinHTTrack is that I am trying to download
images from a site which requires the referer to match the URL each actual
page in the site.  So whereas a referer of <http://www.site/images01.htm> would
work for the images at <http://www.site/images01.htm>, it would not work for
<http://www.site/images02.htm>, etc.

Please add this feature.  I look forward to donating to the project.