how to clear all non-jpg img tags from a string

How to clear all tags from an HTML string from files that do not have a jpg or gif extension in PHP

I have to remove all img tags from a string, where the extension of the src is not jpg or gif.

So far I tried:

$dom=new domDocument;
$dom->loadHTML($content);
$dom->preserveWhiteSpace=false;
$images=$dom->getElementsByTagName('img');
foreach($images as $image)
{
    $ea=array('gif','png','bmp','jpg','jpeg');
    $ext=pathinfo($image->getAttribute('src'), PATHINFO_EXTENSION);
    if(!in_array(strtolower($ext),$ea))
    {
        $image->removeAttribute('src');
    }
}
$cleanc=$dom->saveHTML();

but this is slow and it only removes the source.