If you regularly use flashcards to build your brainpower but find it too easy to cheat or just inadvertently see through the cards, Lifehacker reader Honda Wang uses QR codes for an inventive solution:
I finally found an applicable use of QR codes in education! Before I started using them for foreign language flashcards, it annoyed me that I could see the English word behind the card when I was studying. Now I can't see the English word since it's a QR code!
When he's ready for the answer, he just scans the code with his phone. Not bad!