1) Install a program called HashCheck.
2) Grab BGB (GB/SGB/GBC emulator for Windows PCs).
3) Obtain a legit ROM of English-version Pokémon Yellow.
4) Right-click the .gb file, go to Properties, then Checksums and copypaste the SHA-1 hash after it finishes calculation:
>CC7D03262EBFAF2F06772C1A480C7D9D5F4A38E1
5) If it matches, you're good to go.