Doesn’t matter whether it’s in fiat or crypto, tax agencies consider ANY income taxable.
It’s a pretty complicated subject, especially with the unique dynamics of Steem.
Of course, if you’re conducting all your activity under a pseudo name and haven’t withdrawn any funds to accounts linked to your real identity, you could potentially go undetected. But IF you ever get audited and they find out you weren’t declaring income, you could very well be considered to have committed tax fraud.
Nope, not centralized.