$pattern = "/<img([^>]*) src=\"([^\"]*)\"/";
$replace = "<img\${1} dst=\"\${2}\"";
$text = preg_replace($pattern, $replace, $text);
$pattern = "/<img([^>]*) src=\"([^\"]*)\"/";
$replace = "<img\${1} dst=\"\${2}\"";
$text = preg_replace($pattern, $replace, $text);