Comment 1 for bug 1306396

Currently the only solution/workaround is to crop the image, so that the remaining transparent pixels are reduced to a minimum (concentrate on the key visual aspects being opaque).

The current implementation based on the OpenCV feature matchTemplate does not allow images having a transparency channel - only the 3 RGB channels being taken as opaque.
So transparency information is simply ignored on the way from the given image to the OpenCV Mat object.

BTW: with Sikuli it is a best practice anyway, to take care, that an image contains as little background as possible, thus concentrating on the key visuals of the image. The more even background, the lower the resulting similarity can be.