For context, I'm in the UK, but I suspect the answer will apply regardless of the jurisdiction.
I'm of the understanding that if you buy BTC and then sell for profit at a later date, you're liable for Capital Gains Tax. But what's the tax situation if you're mining coins, and then selling them on your local exchange? My intuition is that it can't be CGT, because you didn't buy the coins in the first place - in the extreme case, you bought a mining rig, which was then used to produce coins, which you later sold. But I find it impossible to believe that you don't have to declare income gained like this. So what does it fall under?
This is a very good point that I hadn't considered. I'd imagine it would be the equivalent to how some CEOs take all or part of their salary as stock which they can then liquidate for cash. Never occurred to me whether that kind of liquidation would qualify as capital gains tax, income tax or some third kind of tax that I'm not aware of... I await a response!
I plan to declare the cost of electricity as an expense, and the bitcoins generated as profit; the net profit will go under self-employment (Schedule SE). I haven't bought any additional hardware, but if I did, I'd list it as a capital expense, take depreciation, etc.