I was trying to go off the example at: 
<http://www.httrack.com/html/fcguide.html>

-*.gif*[> 5] -*.zip +*.zip*[< 10]

Refuse all gif files smaller than 5KB, exlude all zip files, EXCEPT zip files
smaller than 10KB 

I want to exclude all Images smaller than 21K.  Or Only include only Images
larger than 21K.

Here is the issue I ran into:
-*.gif* +*.gif*[< 21]
That should be "no images except images under 21KB",
returns Images larger and smaller than 21KB

When I only run and exclude filter like:
-*.gif*[< 21]
It should return "no images under 21KB",
however it returns no images at all (I only get the HTML files.)