mwryder55 :
Nevada has early voting where a person can vote at specific sites for weeks before election day. They do not have to go to their regular polling station for these early votes. The fact that the votes would be saved inside the Scantrons allows a person to open the machine and change the ballots inside with new ones with the same bar codes but different ballots. Without a copy of the ballots outside the machine there is no way to verify this has not happened.
They don't use normal barcodes. The barcode runs the length of the ballot sheet. The only way to accurately reproduce the barcode is to photocopy the ballot, which isn't possible since they're in sealed packages until they reach the polling station and standard printer paper is much thinner. The only people that have access to the ballots before the package is unsealed, is the company that produces them since the package is unsealed in front of law enforcement. So, what you're suggesting is very unlikely to happen without cooperation from everyone present at the voting station along with the company producing the ballots themselves. Also, it's my understanding that the machines are locked shut and can not be unlocked by anyone at the polling stations and the machines are only unlocked in the presence of law enforcement to ensure no tampering happens. But, I guess anything is possible for the right price....