The way the mocap works is by having a way to map the face in 3D to project it onto the model, which is why it needs an iPhone as they have a depth sensing camera. To my knowledge there isn't a reliable way to retarget from a 2D image and get any decent level of accuracy (although with motion it can sort-of work with a webcam through virtual motion capture/other vtuber apps). You *can* capture a single frame from most of the iphone mocap apps, though.