A canceled check is one that has been paid by the bank and marked as canceled. Canceled checks also prove payment when a recipient claims that he has not been paid by someone that owes him money.
People used to receive printed copies of canceled checks with monthly statements for reconciliation. However, as of 2014, most bank customers receive scanned digital copies of canceled checks that they can review through online accounts. While a canceled check cannot be cashed again, it is a risk for a person to leave out in the open because people who commit identity theft get account numbers and routing numbers from them.