PHP check image alt tag

<?php
// Your code here!
$pattern ='/<img.*?alt="News18".*>/';
 $finaldata= 'this is dummy string <img loading="lazy" src="http://hindicmsrevamp.news18.com/wp-content/uploads/2022/06/1655804926_1614700942_betel-nut-5.jpg" alt="Bappi Lahiri" width="875" height="580" class="alignnone size-full wp-image-4214823"> this is another sentesnces <img src="imagetwo.jpg" alt="News18"/> this is third one';
$doc = new DOMDocument();
@$doc->loadHTML($finaldata);
 $tags = $doc->getElementsByTagName('img');
$val['Keyword']='Bappi Lahiri';
$val['link']='#';
foreach ($tags as $tag) {
       $src=$tag->getAttribute('src');
       $alt=$tag->getAttribute('alt');
        $tag->setAttribute(
   'alt',
   'hihihih'
  );
  $a = $doc->createElement('a');
        $attrib = $doc->createAttribute( 'href');
       }
echo $doc->saveHTML();
//echo $finaldata = preg_replace('/(<img [^>]*alt="'.$val['Keyword'].'"[^>]*>)/', '<a href="$2">$1</a>', $finaldata);
// echo $finaldata = preg_replace('/(<img [^>]*alt="'.$val['Keyword'].'"[^>]*>)/', '<a href="'.$val['link'].'">$1</a>', $finaldata);
?>