The Check Clearing for the 21st Century Act (Check 21) is a federal law allowing banks that process checks to convert them to substitute checks to make the exchange of funds easier. When an original check is processed and an image of your check is created, the original check is usually destroyed by the processing bank. This improves the efficiency and safety of the nation’s check payment system. All financial institutions must comply with this federal law, as of October 28, 2004.