It is hard to reconstruct an animation rig from a selfie with a smile. This is why we and our customers ask consumers to take a photo with a neutral expression. This is not needed anymore.
We have released a function that detects if a person in an input image is smiling, and remove the smile! We digitally replace a smile with a neutral expression. The feature is already available in the Cloud API starting from the Plus subscription, see the remove_smile parameter in the Avatar Modifications section of the documentation. Here are a few examples (from left to right: input image, generated image with a neutral expression, and a reconstructed avatar):