You probably can use an alternation to handle this. try the following:

my $str = <<END_STRING;
<story>
  <page>
    <description> desc </description>
    <image> notExpected.jpg </image>
    <headline> head </headline>
  </page>
</story>
<image>correctImage.jpg</image>
END_STRING

my $ptn = qr{<story>.*?</story>|<image>(.*?)</image>}s;
my @out = ($str =~ /$ptn/g);
print qq("$_"\n) for grep $_, @out;
[download]

You need to do more test by yourself thought.

Regards,
Xicheng