This is a follow-up to this answer by Dawn who explained that anti-ballot-photos laws have been struck down in:
New Hampshire: Rideout v. Gardner.
On the other hand, posting completed ballots is illegal in Wisconsin.
When vote-swapping, without the ability to share photos of completed ballots it's not possible to check whether participants in a vote swap honor their agreements.
Which states allow disclosing photos of one's own voting ballot to a vote-swap partner?