Firefox plugin Tamper data

$allowedExts = array(
    'jpg' => 1,
    'jpeg' => 1,
    'png' => 1,
    'gif' => 1
);
$allowedMimes = array(
    'image/jpg' => 1,
    'image/x-jpg' => 1, // IE
    'image/jpeg' => 1,
    'image/x-jpeg' => 1, // IE
    'image/pjpg' => 1, // Progressiv JPG
    'image/png' => 1,
    'image/x-png' => 1, // IE
    'image/gif' => 1,
    'image/x-gif' => 1 // IE
);

if (is_uploaded_file($_FILES['myPic']['tmp_name'])===true) {
    $ext = strtolower(pathinfo($_FILES['myPic']['tmp_name'], PATHINFO_EXTENSION));
    $type = $_FILES['myPic']['type'];
   
    if (is_string($ext)===true && is_string($type)===true && $allowedExts[$ext] && $allowedMimes[$type]) {
        // Tilladt fil
    } else {
        // Ikke en tilladt fil
    }
} else {
    // Ingen fil uploaded
}