i have this code for our custom amp page in wordpress this code remove our all images in content area but i want these images show as a amp images

$content = get_the_content();
$content = preg_replace("/<img[^>]+>/i", " ", $content);          
$content = apply_filters('the_content', $content);
$content = str_replace(']]>', ']]>', $content);

$content = str_replace("https://www.youtube.com/embed/","",$content);

$content = preg_replace('/<iframes+.*?s+src=(".*?").*?</iframe>/', '<amp-youtube
    data-videoid=$1
    layout="responsive"
    width="480" height="270"></amp-youtube>', $content);                
echo $content;

help me out how to customize preg_replace function to replace tags to <amp images