Looking at the image, I would guess the moulding isn't stuck to the tub. Rather it was built as a part of the housing to hold the tub and marble around it. If you notice the tub is sitting inside the marble which suggests a frame with a drop in tub, instead of a full tub with an exterior.

I don't think you could replicate this look if you have a more stander tub housing, though if you find a way let us know because I love this look.