Either the url tells you, or the headers tell you, or nothing tells you and you have to guess

LWP::MediaTypes, File::MMagic

$ ls -loanh *.gif
-rw-rw-rw-  1 0 53 2010-09-17 23:39 working.gif

$ perl -MWWW::Mechanize -le" $ua = WWW::Mechanize->new; $ua->get('file
+:working.gif'); die $ua->ct; "
image/gif at -e line 1.

$ perl -MWWW::Mechanize -MLWP::MediaTypes=media_suffix -le" $ua = WWW:
+:Mechanize->new; $ua->get('file:working.gif'); die media_suffix( $ua-
+>ct ); "
gif at -e line 1.
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