I like AZ Rep Finchem’s idea about putting an embedded watermark visible only with UV light. Kinda like money so it would be really hard to duplicate. Cost would be $.25 per ballot.
If all 50 states went with the serial numbers and watermarks most of the fraud can be wiped out if the ballots are available for inspection by bonded representatives from any party or citizens group. A spot check of 1000 sample ballots picked out at random would be a good start and would not take long.
I read that, its the best and most comprehensive plan I have heard of. Probably why it seems to be going nowhere. It would be a game changer.