So, based upon the IRS's classification of Cryptocurrency, all crypto is treated as 'property'. Thus, to me I feel that everything generated through posts will be treated as income. As such, the income will be recognized as taxable immediately upon receipt. This will then establish a basis for which any gains/losses will be based upon.

So, for example, you get 10 STEEM, each worth $10 for a total of $100. The $100 will be recognized as income and taxed accordingly. This establishes a basis of $100 for the 10 STEEM. Now, say the value rises $1 (from $10 to $11) per STEEM. Now you have an UNRECOGNIZED gain of $10 ($1 * 10 STEEM). However, this gain will be recognized in the instance of 1) you cash out your STEEM or 2) you exchange the STEEM for any other cryptocurrency.

Again, I am not a tax specialist and this is very new area with an interesting set of circumstances. This is just my opinion and should be taken as such. Let me know if you have any further questions!