$re = '/<span><img (id=\"([^"]*)\").*><\/span>/';
$str = '<section>
<span><img id="id1" src="src" alt="alt"></span>
<span><img id="id2" src="src" alt="alt"></span>
</section>';
preg_match($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