Some of the places with the highest levels of distrust on electoral authorities and government bureaucracy solve this problem by marking your thumb with indelib

Some of the places with the highest levels of distrust on electoral authorities and government bureaucracy solve this problem by marking your thumb with indelible ink, which can't be washed off but fades away over the course of a week or so. This guarantees people enter polling stations only once, even if they magically happen to have been registered at multiple places. We use this in Mexico, in addition to (non-digital) fingerprint-carrying voter ids. Historically, it has not prevented fraud in general (most of which happened due to insufficient audit procedures and rural polls not having observers from all parties, allowing for stuffed ballots and the like). It did however close that particular attack vector. My trust on the results of an individual polling station in an urban area with observers from all major and most minor parties is actually quite high, even as I know any or all of the observers involved are likely to be corrupt and have low regard for the law. The reason for this is that they are all incentivized to prevent each other from cheating and have the means to detect tampering in such setting (without needing uncommon expertise beyond observation and basic arithmetic). https://en.wikipedia.org/wiki/Election_ink https://en.wikipedia.org/wiki/Election_ink