Codice PHP:
<?php
$string
='[img]ciccio.png[/img]';

preg_match('/<img.*src=(\'|")(?P<img_link>.[^\'"]+)(\'|").*>/i',$string,$out);

print_r($out);
?>
ma il forum sega i backslash...

il codice pulito è

<?php
$string='[img]ciccio.png[/img]';

preg_match('/<img.*src=(\'|")(?P<img_link>.[^\'"]+)(\'|").*>/i',$string,$out);

print_r($out);
?>