The missing thumbnails, as far as I can tell, seem to be png files which I
think I included in the the scan rules. 

I have found that I can edit the html and use a jpg image in it's place and it
works when I view the mirrored page.

below is the doit log file. I only changed the site name in the log.  

Does the log show a reason why the png images don't work? 

"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" -%F "<!-- Mirrored from
%s%s by HTTrack Website Copier/3.x [XR&CO'2010], %s -->" -%l "en, en, *"
<http://someweb.com/> -O1 "L:\\Someweb\\Someweb-Zip\\Someweb Albums Mirror"
+someweb.com/* +*.css +*.js -ad.doubleclick.net/* -mime:application/foobar
+*.gif +*.jpg +*.png +*.tif +*.bmp +*.zip +*.tar +*.tgz +*.gz +*.rar +*.z
+*.exe +*.mov +*.mpg +*.mpeg +*.avi +*.asf +*.mp3 +*.mp2 +*.rm +*.wav +*.vob
+*.qt +*.vid +*.ac3 +*.wma +*.wmv
File generated automatically on Thu, 22 Mar 2012 09:22:45, do NOT edit