<?php
class F_FileIterator extends FilterIterator {
	private $ext;

	function __construct(DirectoryIterator $it,$ext) {
		parent::__construct($it);
		$this->ext=$ext;
	}

	function accept() {
		return in_array((pathinfo($this->current(),PATHINFO_EXTENSION)),$this->ext);
	}
}

$d=new F_FileIterator(new DirectoryIterator('ПУТЬ ДО ПАПКИ'), array('gif','png','jpg','jpeg'));

$count=0;
foreach ($d as $v) {
	$count++;
}

echo "В папке $count графических файлов";
?>