The fare inspectors should be able to photograph an offender to give a warning for the first time. If on a second offence, they get a "hit" with a photo, they are given a "small" fine. On subsequent offences, the "fines" increase on each "hit". When the offender "hits a threshold", the police should be called. We could "erare" the "hits" after a passage of time, like a couple of years. (Twins, triplets, up to nonuplets, or doppelgangers, may need additional identification.)
If customs (at airports and land crossings) uses facial biometrics, so should the public transit fare inspectors.