The underlying technology is called diffusion models. I'm sure many on HN have already hear of it - it's the technology underlying all these neat text to image results in DALLE-2, Imagen, and the open source counterpart called Stable Diffusion.
Getting this technology to embed real life images in arbitrary backgrounds has been quite the challenge, but it's already showing some pretty neat results which you can check out on the website. Currently we support Christmas setup, and white background with shadows and reflections. We'll add a plenty more background categories in the immediate future.
Couldn't help but notice you omitted any reference to the major technological achievement here in placing objects on arbitrary backgrounds. It failed to impress on your use case?
I did a few images and it was interesting. I suspect, if I pick the right background and and the right images then this would be very handy at scale. As a solution, besides how it's accomplished, the tech, how does this differ from using GIMP's API to merge two images? I guess that's what I'm missing.