A lot of us (who have bank accounts, unlike the tunnel dwelling UNKewlJ) have been depositing paper checks via Mobile Deposit. (When we get paper checks - these are getting more rare as electronic transfers (such as he fictional one FraudJ tried to fantasize about in his backrooming fable) become the norm.) Most of my banks allow up to a $25,000. single day's deposits, and $150,000. for the month.

What I always wondered was - what is to stop someone from depositing that piece of paper again, especially at a different bank?

Well, now I know how the system works. The other day I deposited a dozen checks I had received, all via mobile, and one of them was rejected. I received the emailed rejection notice a couple hours after making the deposit. It did not state why the deposit was rejected, just that it had been and that a letter was coming in the mail explaining why.

I assumed I should just re-deposit it, same bank, but when I tried the system immediately told me that this item had already been deposited once and would not accept it.

The next day I was going to just mobile deposit it into another bank, or take it to the ATM, but I decided to call the bank to ask why the deposit had been rejected. In the process of that phone call, they told me that once a mobile deposit is made, if accepted - and even if later rejected, the banking system starts notifying all banks in the entire Federal Reserve system that this item has been deposited, such that it will be rejected if re-submitted anywhere. So I was told that to get this particular paper check cleared, I would have to take it to a teller at one of my banks, and tell the teller that it had been mobile deposit rejected, and have the teller note the deposit in that way to make sure it went through.

When I did that, the teller asked me where I had mobile deposited it (which bank), made some notes, and accepted the deposit. So far, so good, the deposit was credited the next day.

Anyway, just interesting to me how this sort of thing works. I remember when we were teenagers some of my friends, desperate for money, would try all kinds of crazy things with their bank accounts to try to get cash out of the ATM, including deposit blank pieces of paper or empty envelopes while punching in some figure to the ATM machine to claim that an actual check was being deposited. Of course nowadays that won't work the ATMs all scan the cash or check for verification and there is no envelope used any longer.

One thing that hasn't changed much is that the ATM or mobile deposit system doesn't always read the check that closely other than the MICR line and the dollar amount. You can still get away, most of the time, with sticking a check that isn't even made out to you (such as if made out to a different company you own) into the system, or neglecting to endorse the back. But, the system is getting better at examining those details and looking for at least a scribble on the back on the check.