How about a stately, classic bank building engulfed in flames.
A spreadsheet would be a closer representation of Bitcoin. You can make it a paper one if you want a proper photo :)
But does a spreadsheet icon look like a currency to you?
Well, since it's a crypto-currency, maybe something cryptographic? But I see the point, people associate currencies with coins.
How do you visualize cryptography? A padlock? It might be a cool image to have a stack of those "B" coins with holes punched through them attached to a lock. I don't know if that would really help describe what bitcoin is though.
A police officer peaking around his blindfold at an ostrich with its head buried in the sand?