Put it down in a simple way, the issue arises when the U.B.O. gets the money in his/her own account in the country of residence. Before that moment, they're just a crypto inside an account. The problem, in the end, will be identified not when you receive a reward for an article, but when you have converted BTC to FIAT in your Coinbase (i.e.) and transfer them to your bank account. At that point you need to refer to the jurisdiction of the country, one thing could be to officially ask the question to the Inland Revenue Dept. Here - but I say here and not elsewhere - after 60 days without a reply from a public office you're authorized to proceed and consider it as a go (silence is confirmation rule). It may be considered as a capital gain or interests. There's still debate if the BTC is money or not, go figure.