It depends on the country, obviously. In my one there is no clear legislation, but the most likely scenario is that you have to declare them as if you were being paid for being a freelancer writing for a newspaper or a magazine, so your earnings here counts for your income tax.
There is no legislation as well in my country so whenever I sell my btc for our local currency, I do not pay any taxes except for the fees in the exchange. Since income tax should apply regardless of what currency it is, once declared there may be some taxes imposed for btc that is exchanged. As long as it's part of your income, you would have to pay taxes as well.
It's best to find out first what is the legislation in your country regarding bitcoin and cryptocurrency and whether regulations are made for it.
Yes it is true if we successfully transmit btc sales results that we give taxes to the government because the rules are the rules that must be enforced as good citizens we must comply with absolute government regulations. But now how to make the sale btc can be made a valid tax?