What happens if you don't claim Bitcoin on taxes?

Good day, I'm curious about something regarding Bitcoin and taxes. If an individual were to acquire Bitcoin, let's say through mining or a purchase, and they fail to report it on their taxes, what would be the consequences? Could they face penalties? Would the unreported Bitcoin be subject to seizure by the tax authorities? And how would the tax authorities even know about the unreported Bitcoin if it's kept off the books? I'm just trying to understand the implications of not claiming Bitcoin on taxes.