//I use preg_replace_callback which calls a user defined function ever time it finds a match. In that function I check the $firstTime global variable. If its set it won't blank out the img. Afterward I search and remove any empty <a> tags.

<?php
$string = $item->get_content();
$firstTime = true;
$pattern = '/<img[^>]+?[>]/is';
$string = preg_replace_callback($pattern, 'imgOff', $string);

// remove empty <a> tags
$pattern = '/<a[^>]*?[>]<\/a>/si';
$replacement = '';
$string = preg_replace($pattern, $replacement, $string);
	
function imgOff($matches)
// remove all but first img tag
{
	global $firstTime;
	if ($firstTime)
	{
		$firstTime = 0;
		return $matches[0]; // skip first img tag
	}
	return '';
}
?>