#<img border="0" src="/images/wink.gif" alt="Wink">

# Match <img, followed by a minimum 38 and a 
# maximum 50 of any characters before reaching
# the specific target word

$body =~ s/<img.{38,50}="Smiley">/:)/g;
$body =~ s/<img.{38,50}="Wink">/;)/g;