Doing this without user accounts will make piracy rampant. Someone will figure out your hashing scheme, as you've shipped them the code to check it. Is no user accounts, and no registration server really the way to go?

If so, maybe QR codes, key files?

How about a hash to "correct horse battery stapler" converter? Get a list of 4096 unique words, so 12 bits per word, and make the key three words.