I just tried adding the lines:

$image2->Set(type=>"TrueColorMatte");
$image1->Set(type=>"TrueColorMatte");
[download]

before doing the image composition, and it's still not working - however I set the composition mode and opacity, I can't make it do a semitransparent overlay.

So unless I missed the point of what you were saying, this doesn't seem to be the answer.

Andy Baxter.