I think if the flames holds the private key itself, will be impossible to decode it without the rest of the picture, because if it could be decoded only with operations over the flames, paiting the chess board and the other pieces will be a waste of time for the creator. I think that the chess board is too full of symbols to be only a distraction...

I'm saying this because over the whole thread the flames kept 80% of the attention, and I'm not talking about the 10000% zoom things, the jpeg glitches or the rabbit, simply the pieces and their meaning.