how to get avatar of an user ?

My goals is simply to start a BLANK page with a logged user (I can get the $_COOKIE) to get the loggedon user.

How do I get the avatar of this userid ?

I found that which is very useful:

But what libraries should I include in my blank.php page ? 

// This one gets the 32x32 small avatar.
$upic = $GLOBALS['oFunctions']->getMemberAvatar( $iId, $sType = 'small' );

// This one gets the 64x64 standard size avatar.
$upic = $GLOBALS['oFunctions']->getMemberAvatar( $iId, $sType = 'medium' );