<pre> 
<?php 
$s = '<img hspace="4" vspace="4" border="1" alt="Nagoya Institute folding X-Frame car lacks S-foils, hyperdrive, rolls on a big orange ball" src="http://www.blogcdn.com/www.engadget.com/media/2010/09/x-frame-2010-09-02-600.jpg" /> 
<img src="http://media02.hongkiat.com/speed-performance-check/pingdom.jpg" alt="Pingdom" border="0" title="18 Website Speed and Performance Checking Tools" />
<img width="200px" height="100px" src="http://blog.makezine.com/upload/2010/09/vice_grip_with_more_cowbell/expand-o.jpg"  alt="expand-o.jpg" />';
$img=preg_replace('/ width="\d+" height="\d+"/', '', $s);
echo $img;
?> 
</pre>