$re = '/(?:<img|(?<!^)\G)\h*(\w+)="([^"]+)"(?=.*?\/>)/im';
$str = ' <img src="abc.png" alt="abc" />
<img alt="def" src="def.png" />
<img src="abc.png" alt="abc" style="border:none" />
<img alt="def" src="def.png" style="border:none" />';
preg_match_all($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