I have two 256X256 images, one has full purple background and the other has some of it transparent.
I want to copy the second image into the first image, so that the transparent data from the second image is filled by the data from the first image, resulting this:

My attempt of doing so ended with the entire first image replaced by the second image. I used the OverCompositeOp
operator:
MagickCompositeImage(wand1, wand2, OverCompositeOp, MagickFalse, 0, 0);