I don't think mining would be the proper legal term by any means, but assuming it would, then you would be producing a commodity, otherwise, considering that a finite number of bitcoin will exist, one could argue that they already do exist, and as such, nomenclature aside, you are finding/recovering unclaimed currency, which would be income when you find it.  I'm not recommending this, but here is another argument for it being income: when mining, you are providing (proof of) work for pay (mined coin and/or fees), it just happens that the entity controlling that pay is a peer to peer network that will always net 0 income and loss.