在php问题中将图像保存为jpg

Having code to display image like:

header('Content-Disposition: attachment; filename="aaa.jpg"');

header("Content-type: image/jpeg");
echo $row['pageurl'];
}
else
{
echo mysql_error();
}

Problem,is every time it saves images as aaa.jpg(name i have given),now i want to save with different name each time as 1111.jpg gdfgfdg.jpg or randomly.How to do that?