I think what you're after is something like this:

my $body = qq!<img border="0" src="/images/wink.gif" alt="Wink"> <img 
+border="0" src="/images/smiley.gif" alt="Smiley">!;

%replacer = ( "Smiley" => ":)",
              "Wink" => ";)" );

$body =~ s/<img(?:.+?)="(Smiley|Wink)">/$replacer{$1}/g;

print "$body\n";
[download]

which prints: ";) :)" -- note that it uses "(?:.+?)" to cluster, not capture, the irrelevant characters that precede the "=".