<?php
$text = '<p>Hi, this is a test, here is an image<img src="http://m...content-available-to-author-only...e.com/beer.jpg" width="60" height="95" /> Because I like Beer!</p>';
$domDocument = new DOMDocument;
$domDocument->loadHTML($text, LIBXML_HTML_NOIMPLIED|LIBXML_HTML_NODEFDTD);
$imageNodeList = $domDocument->getElementsByTagName('img');
 
foreach ($imageNodeList as $Image) {
      $Image->setAttribute('src', 'lalala');
      $domDocument->saveHTML($Image);
}
 
$text = $domDocument->saveHTML();
echo $text;

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