A bit more context from someone who was involved on this. While it doesnt cryptographically eliminate the possibility of tampering from the moment a vote is cast, it greatly reduces the window of possible tampering to a few short moments between when the witnesses sign the physical tally sheet and when its scanned and the jpg is made available on the server.

The goal of this project was to build on the existing paper ballot + physical witness system in Guatemala and what opentimestamps made possible, by actually running a citizens' audit, in a relatively low cost and reproducable way using Stakwork. Stakwork was a good fit for this as it allowed us to break up each tally sheet into microtasks in a blind AI-human consensus using open source models and anon Stakworkers, most of which signed up during the audit on fiscaldigital.net

Heres a presentation from Adopting Bitcoin conf late last year explaining the process in more detail: https://youtu.be/eyvfGnlzXqo?si=qsNpFpuXb-4rdbtc