If you want to remove image files from your awstats reports, modify the SkipFiles variable in the /etc/awstats/awstats.conf (or awstats.YOURHOST.conf)
Do a search for “SkipFiles” in the file using nano/vi/emacs and find the section that talks about “Use SkipFiles to ignore access to URLs that match one of the following entries…” The SkipFiles line should look similar to the following:
SkipFiles="REGEX[.jpg$] REGEX[.gif$] REGEX[.png$]"