$re = '/(\[(img|\w{4,})\][\s\S]*?\[\/\2\])(\n?)|([\s\S]+?)(\n?)(?=$|\[(?:img|\w{4,})\])/i';
$str = 'Cum haec taliaque sollicitas eius aures everberarent expositas semper eius modi
rumoribus et patentes.
[image]https://foo.com/fighters.png[/image]
Denique Antiochensis ordinis vertices sub uno elogio iussit occidi ideo efferatus,
quod ei celebrari vilitatem intempestivam urgenti, cum inpenderet inopia
[image]https://foo.com/fighters1.png[/image]
[image]https://foo.com/fighters2.png[/image]
Utque proeliorum periti rectores [i]primo catervas[/i] densas opponunt et fortes,
deinde leves armaturas, post iaculatores ultimasque subsidiales acies, si fors
adegerit';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($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