If you're earning rewards here on Steemit, for US income tax purposes, it's considered revenue which has to be reported at fair market value in the year teh reward is earned. That also becomes your basis for when you trade out of crypto and into USD to determine your capital gain. It's actually got two steps, not just one.

I have a whole series called US Tax Considerations on my blog where I go into it in more detail. My most recent was about capital losses from trading crypto.