$re = '/<img src=".*?\/([A-Z0-9]+)\.\w+"\s*\/><img src=".*?\/([A-Z0-9]+)\.\w+"\s*\/>/m';
$str = '<img src="http://www.example.com/app_res/emoji/1F60A.png" /><img src="http://www.example.com/app_res/emoji/1F389.png" />
<img src="http://www.example.com/app_res/emoji/1F61E.png" /><img src="http://www.example.com/app_res/emoji/1F339.png" />';
$subst = "&#x$1; &#x$2;";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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