The ballot's serial numbers, as well as the invisible codes, have all been created and recorded by voting officials before the election to eliminate the possibility of ballot-box stuffing. If any would-be fraudsters tried to create and fill out fake ballots, they could easily be thwarted: Even if they were able to replicate real serial numbers, there's virtually no way the forged ballots' invisible codes would match those on the real ballots.
If you decide that you want to check and make sure your vote was counted correctly, you can write each of the now-visible codes on your receipt, which you detach from the ballot and take with you. The rest of the ballot you hand to election officials, who immediately scan it with an optical scanner, recording your vote in a database.
Once you leave the polls, you can access a designated election website and log in to a public database. Then you enter your ballot serial number and a list of your invisible ink codes appears on the screen. (Only the "secret" codes will be in the database, not the names of the candidates themselves—that way, hackers can't see who you voted for, so your vote remains private, and no one can change your vote online.) If the codes in the database match the codes you wrote down, your vote was indeed counted correctly.
And if you don't want to go to the trouble of hitting the Internet after you vote, don't worry: You can trust that enough other people—including bloggers, political staff members, and just about anyone in the main stream media—will. And they should be enough, according to Chaum and his team: If only one or two percent of voters check their receipts, it will create a 95 percent chance that no fraud occurred. Just imagine if all of us got into the act.