Right, otherwise the problem would be trivial. If it wasn't clear, the plan was the printed ballot would anonymously go in a box to be machine counted.
Yup, but they can do so with old-fashioned paper ballots too. Any security measures for paper ballots will also work with my idea, and the machine could also do fancier things like printing out a timestamp and signature of the timestamp . I really want things to be simple though: if the system of voting is too complex, then it will be distrusted, and distrust in the voting system is toxic to democracy.
What they can't trivially do with any system including paper ballots is remove ballots, compared to digital voting machines where you can add e.g. -100 votes to candidtate A, 100 votes to candidate B, thus ensuring that the total-votes field is correct while advantaging candidate B -- this was actually demonstrated by a security researcher on a Diebold touch-screen machine.
