In 90% of the case it's more or less the same.
You buy bitcoin, ok.
Your btc value rises, cool for you.
You sell your btc at a higher value? HERE you have to pay taxes on what you won.
There are specific rules on your country after that but in msot cases you'll pay only on what you earned.
Yeah, that's true and that's called capital gains
On which you should pay a capital gain tax, a sort of income tax. On the other hand, seeking advice from authorities may actually move the government to pay special attention to Bitcoin, and the outcome of that may not make you quite happy (in respect to the amount of taxes you may have to pay, in the very least). Indeed, a small number of such appeals won't raise enough suspicion but if many folks start asking, everything may change. In other words, don't trouble trouble until trouble troubles you