I'm going to ignore the horrible usability issue in this answer and just focus on the title question here.
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One idea is to generate a visual fingerprint like OpenSSH visual fingerprint. OpenSSH Visual fingerprints produce blotch of ASCII characters that are supposedly somewhat memorable can be quickly compared visually.
If you want to be slightly fancy, there's the Aestheticode. Aestheticodes like Penguin Barcode can be scanned, is distinctive and aesthetically pleasing, and is fairly easy to visually compare without a machine. Problem is that aestheticode are short and most aestheticode are generated manually; you'll need to be able to procedurally generate these images if you're going to do this everyday.