basic PHP image proxy (that works ... )

imageProxy.php

<?php

    $url = "";

    if( isset( $_GET['url'] ) )
    {
        $url = $_GET[ 'url' ];
    }
    else
    {
        exit();
    }

    $imginfo = getimagesize( $url );
    header("Content-type: ".$imginfo['mime']);
    readfile( $url );

?>

Completely insecure (...php?url=/etc/passwd)

Thanks!
I've made some validations and security checks in this version: https://gist.github.com/xxnoobmanxx/89329fa61997b3775487b0c155cda41f