function image_callback ($image, $operation
{
/* perform a series of transformation on an image */
switch ($operation) {
case "flip"
$image = flip_image$image, "vertical");
break
case "skew"
$image = skew_image$image, 0.5);
break
case "invert"
$image = invert_image$image);
break
}
$ret = array();
$ret"return"] = $image
$ret"handler"] = HANDLER_IMAGE;
$ret"arguments"] = array$image);
return $ret
}