How to use a png watermark?

[petervg]

I want to add a watermark and use a png (which is transparent). The transparent png parts show up as white areas on the image. Is there a way to use transparency in the watermark while keeping the opacity to 100?

I've attached an image of the current output as an example. The watermark is at the bottom right.

[xnview]

is it a 8bits+alpha png? if yes, it's not supported, only PNG+transparency or RGBA PNG