Make img AMP-ready

ampify_img.php

<?php
/**
 * Replace img tag with amp-img
 *
 * <amp-img src="[src]"
 *   width="[width]"
 *   height="[height]"
 *   layout="responsive"
 *   alt="[alt]">
 * </amp-img>
 *
 */
function _domradio_util_ampify_img ($html) {
  preg_match_all("#<img(.*?)\\/?>#", $html, $matches);

  foreach ($matches[1] as $key => $m) {
    preg_match_all('/(alt|src|width|height)=("[^"]*")/i', $m, $matches2);
    $amp_tag = '<amp-img ';
    foreach ($matches2[1] as $key2 => $val) {
      $amp_tag .= $val .'='. $matches2[2][$key2] .' ';
    }

    $amp_tag .= 'layout="responsive"';
    $amp_tag .= '>';
    $amp_tag .= '</amp-img>';

    $html = str_replace($matches[0][$key], $amp_tag, $html);
  }

  return $html;
}