proc watermark(img: Image; watermark: Image;
               verticalAlignment: VerticalAlignment = VAlignCenter;
               horizontalAlignment: HorizontalAlignment = HAlignCenter;
               opacity: float = 0.5; margin: int = 20): Image {.
    ...raises: [VipsError, ValueError], tags: [], forbids: [].}

proc watermark(img: Image; watermark: Image; x, y: int;
               opacity: range[0.0 .. 1.0]): Image {.
    ...raises: [ValueError, VipsError], tags: [], forbids: [].}