Foot Recognition and Tracking - Augmanted Reality

Hi, first of all, sorry for my English.

I have mentioned my question on the title. I want to develop an app that can tracking foot by camera and put 3D shoe object on it but I couldn't find the best way to do it. I have enough experience in Unity and augmented reality. I guess I have to improve my OpenCV skills to complete this project.

Do you have any idea how to do it? I researched for assets. Vuforia's object recognition seems not enoug for this. Also there are opencv projects can track face and put a mask on it or track hands.

https://wanna.by/

As you can see, there are apps which can track foot, nail or finger. What should I learn to make a simple version of these apps?

Thank you for reading. I appreciate your helps.

Ps: I can pay any price for an asset or library which able to do these features