It works best when you have many rings and few on-hand photos. Jewelry stores often carry dozens of designs, and a macro shoot with a hand model for each one is expensive, so usually only the bestsellers get on-hand images.
With the AI ring try-on you can give every ring an on-hand image and show it on different genders, ages and skin tones. A normal photo works; no transparent PNG is needed.
When you upload a hand photo, use only your own photo or one you have permission to use, never a public figure, and keep other rings off that hand. If the finger already wears a ring, the model tries to replace it, so check for leftovers.
Before a result goes live, check four things in order: the stone, the setting and prongs, the band and metal, and the hand and finger.
If any of them is off, keep the ring photo loaded, pick another hand or add a short note such as “keep the six prongs” or “wear it on the index finger”, and generate again.
Stone macros, inside hallmarks, setting height and real sparkle are still best shown in real photos.