I'm working on a python web service.
It calls another web service to change the picture of a profile.

It connects to another web service.
This web service can only accept pictures that are 4 MB or smaller.

I will put the checking in the first web service.
It uses PIL to check if the base64 string is a valid image.
However, how do I check if the base64 string will create a 4 MB or smaller image?