Unable to test right now, but this should work:

use HTML::Parser;

HTML::Parser->new(
                    default_h =>
                    [sub {
                       print shift;
                     }, "text"],
                    start_h =>
                    [sub {
                       my ($text, $tagname,$attr) = @_;
                       return print $text unless $tagname eq "img";
                       if ($attr->{alt}) {
                         print "[image: \"$attr->{alt}\"]";
                       } else {
                         print "[image]";
                       }
                    }, "text,tagname,attr"],
                   )->parse(join "", <DATA>);

__END__
<IMG SRC="foo"><BR>
bar bar bar<BR>
<IMG SRC="foo" alt="bar">
[download]

-- Randal L. Schwartz, Perl hacker