test

$text = '[divs][center][size=150]Hunter x Hunter[/size][/center][/divs]

[columns1][center][size=150]Poster[/center][/size][divs][center][img3=http://images3.wikia.nocookie.net/__cb20121012124652/hunterxhunter/images/4/40/Hunter-X-Hunter-2011.jpg]Poster[/img3][/center][/divs]';


$posttext = substr($text,0,400);
preg_match('/img3=(.*?)]/msu', $posttext, $icon);
$theXimage = (!empty($icon[1])) ? $icon[1] : '';
if (strpos($theXimage,'.jpg:') !== false || strpos($theXimage,'.jpeg:') !== false || strpos($theXimage,'.png:') !== false || strpos($theXimage,'.gif:') !== false || strpos($theXimage,'.bmp:') !== false)
{
   $theXimage = substr($theXimage, 0, strrpos($theXimage, ':'));
}

echo($theXimage);