I don't know about unity, but if it's like Godot, it can display images. and it can use 2D sprite images to display as 3D object. so it has more potential.
But choosing a game engine it depends on your game genre. Renpy is a simple way to start with and is suitable for visual novels or even point-and-click gameplay. (Actually, Renpy can do more because Renpy is based on Python.)
Not sure if Renpy imports OpenCV for interacting with players. (Just an idea hahaha.)