I really have no clue how to do this, and any help is really appreciated!

I'm hoping to have a page called 'avatar.php' that generates the images, so I can do this:

$hat="headset.png";
$color="blue.png";
$face="normalhappy.png";
echo '<img src="avatar.php?color=$color&face=$face&hat=$hat"> '; // this the 3 in 1 image