XnView Software

The need has occasionally arisen to apply all loaded images to a fixed background image, rather than a fixed watermark to all loaded images.

Since the watermark function may be used to apply a 'watermark' image equal in size to a loaded image, it should be reasonably easy to add an option to select either the existing watermark function, or the inverse process.

Reference: Add custom background to pngs.

+1

I think this could easily be achieved by adding only a z-axis offset to watermark image, eg via checkbox:
☑ Use as background