I just got a $20 from an ATM that appears to be a misprint. I called the bank and they say it sounds like a real bill with all of the security features. The front and back don't line up and they are different sizes. The bill is the old style, small Jackson head, no Jackson watermark and not color changing. I hope someone can tell me something about this bill.
Keep it. You will find a collector that will pay more than $20 for it. You wont make millions, but I wouldn't spend it till you find out more.