I made a series of posters that I often hang around the room when I facilitate workshops. It's fun for participants to get up and scan them at break time. Each poster features a quote about education or technology. Part of the quote or its author is missing and has been replaced with a QR code.
You examine what's on the poster and guess to yourself what the QR code might say. After you have a guess, then scan to see the answer. My favorite scanning app is i-nigma, and you can get it for iOS and for Android.
You can see 20 of the quotes by clicking through the gallery below.