> I found that many of those small size jpg weren't 
properly 
> downloaded by httrack, the warning message is always:
> 'Warning:  File not parsed, looks like binary: 
xxxxxxxxxxx'
> and they are corrupted!!

Generally due to html-tagged jpg files - can you give the 
bogus URL?
(This will work with stupid browsers (IE..) which re-scan 
the file AFTER receiving the MIME type ; but not with 
others like Netscape or Mozilla.)