$re = '/\[img\](.*?)\[\/img\]/i';
$str = 'http://pt.wikipedia.org/wiki/Erich_von_D%C3%A4niken]Erich Von Daniken[/url][/align] [align=center][img]http://www.ceticismoaberto.com/wp-content/uploads/2012/04/erich_von_daniken_7.jpg[/img]';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php