Util.getValidImages should support GIFs with Overlays.
A possible way of doing this is to iterate through each subimage, overlaying the next over the previous.
Java ImageIO does not support this directly - it seems you have to write the overlay yourself, just like how you have to handle your own animation.
The current ImageIO methods in place are probably suitable and the right way of doing it. There just needs to be some additional code to incorporate the overlay.
