An Image to a Pixmap

I want to be able to draw Images inside shapes with bits that aren't in the image to not be drawn. I think I should be using pixmaps and in particular CreateStaticPixmap. I have:

Image = LoadImage(ImageFile)
	ImagePtr = Varptr(Image)
	
	ImagePix = CreateStaticPixmap(ImagePtr,ImageWidth(Image), ImageHeight(Image),

Which I think should work (although I've never used pointers or pixmaps before) but I don't know what I should use as the pitch or format?

Thanks for any help
Matthew