The Frog Prince was one of several adaptations of Brothers Grimm fairytales that Lotte Reiniger made in London between 1953 and 1955: others include The Gallant Little Tailor, Hänsel and Gretel, Sleeping Beauty, Snow White and Rose Red and The Three Wishes.
Here, the frog's regal status is clearly indicated by his tiny crown, though in all other respects he's presented in well-observed and convincingly amphibian form, leaping optimistically after the princess in the belief that she intends to honour her part of the bargain that they struck when her beloved golden ball fell down the well.
The more complex narrative elements are generally downplayed (the prince casually explains that he'd been changed into a frog, without saying who was responsible, or what he'd done to deserve it) in favour of a series of highly visual set-pieces, including the ball's slow descent into the well (the background becoming a watery shimmer) and the frog's dance on the dining-table.
But the story's main moral point - how essential it is to keep one's promises - is forcefully made, the king clearly regarding this as being more important than any private qualms about the wisdom of inviting a talking frog to a private family dinner.
*This film is included in the BFI DVD compilation Lotte Reiniger: The Fairy Tale Films.