<?php
// defining the input
$e = 
'<div class="topbar-links"><div class="gravatar-wrapper-24">
<img src="https://w...content-available-to-author-only...r.com/avatar" alt="" width="24" height="24" class="avatar-me js-avatar-me">
</div>
</div> <img test2> <img test3> <img test4>';
// defining the regex
$re = "/<img.*>/U";
// put all matches into $matches
preg_match_all($re, $e, $matches);
// start creating the result
$result = "<p class='images'>";
// loop to get all the images
for($i=0; $i<count($matches[0]); $i++) {
	$result .= $matches[0][$i];
}
// print the final result
echo $result."</p>";

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