My bank tells me to destroy it when they notify me that the mobile deposit has been accepted.
Some banks use a third party to service the ATMs and they do some of the processing, apparently.
True story: One Friday in 2008, I had a large expense check for several $K. This was before phone deposits, of course, so I went to a drive-up ATM. I got to the point where it wanted me to insert the check and realized I hadn’t signed it. Since it was for so much, I figured I probably should, just to avoid hassles. So I grabbed a pen, signed it, and…just as I inserted it into the slot, the ATM timed out.
Here’s what was weird: the mechanism had detected the check and started running, so it sucked in the check and said “timed out” and ended the session! Dumbfounded, I parked and went into the branch. The manager had never heard of this, and suggested that it would probably turn up, since I had put the account number on the back as well.
It did not. On Tuesday I returned and talked to the same manager, who remembered me. She asked me to call her the next day, which I did; she said they’d done a search and there were NO checks for that precise amount processed since Friday. She also told me that a third party was responsible for removing checks from their ATMs, and that they would check them against the ledger to make sure the amounts matched (of course someone had to, so you didn’t deposit a $100 check and claim it was $10,000; I imagine this is automated today).
Her assumption was that they had found this check with no provenance–since the transaction was cancelled–and just shredded it. Fortunately my company was small and had no problem reissuing the check, so it all worked out OK.
That also happened to be the weekend that Wachovia melted down and sold out to Wells Fargo, although I doubt this had anything to do with what happened. I did notice that the staff were in somewhat of a tizzy when I went back on Tuesday!
ETA: I tried to repeat this several times, with MUCH smaller checks, and was unable to. So it was either a super-narrow window, a malfunction, or it happened to get fixed shortly after my incident.
I have on occasion deposited a handwritten check and had the ATM tell me it could not read the amount and asked me to type it in. I’m sure those are flagged and they verify the amount.