Minimum Requirement Of OpenCV for Facial Recognition Using Python

I want to use a raspberry pi4 for my project but i am confused between whether to go for the 2gb ram version or the 4gb ram or even higher?if there is anyone having worked on similar project , your input would be much valued.

Facial Recognition

what exactly do you mean here ? detection ? classification ? verification ?

I want to use a raspberry pi4

i cannot help, but
maybe you can estimate memory requirements on a different machine, before ?