How does AFUWIN detect that the dump was edited?

I am working on a C++ program right now to automatically change some data in AMI BIOS dumps. How does AFUWIN validate the BIOS dump? Because I don’t see a file signature but some of the people who tried it could only flash the unmodified dump version (without /GAN). I just wanna know if there’s some kind of algorithm or anything like that in the HEX data itself.