PHOENIX - This week, in a congressional hearing, behind Federal Reserve chair Janet Yellen was a “Buy Bitcoin” sign.

The man holding it -- known as CryptoEthan -- helped boost the exchange rate when the photo went viral.

So what is Bitcoin?

Bitcoin is a digital currency. Think of buying into Bitcoin like buying into gold. The price of gold goes up and down depending on the market and depending on when you buy it, you can make money or lose money.

"I saw Bitcoin go really high in value and then drop in value," said Austin Craig, who first invested in Bitcoin years ago, "and a lot of people were saying 'That’s the death of it.'"

Craig is a filmmaker-turned-Bitcoin expert. He has been studying it for years and just released a documentary on the new currency.

"Anybody can contribute," he said. "Anyone can look under the hood and see how it works and that, I think, is the real strength."

For him, Bitcoin has been worth the investment. In 2013, the digital currency was worth about $13.96. Today, it's valued at more than $2,200.

"Every time you do a transaction you get a different code," said Bobby Sharp, the co-founder of Coinsource, the largest Bitcoin ATM network in the U.S.

Sharp put in an ATM inside D&S Market near 32nd Street and Thomas Road.

"So I throw in my $5 bill," he said. "It’s going to give me the equivalent of what that is."

Adam Boyd, an attorney with Radix Law in Scottsdale, warns some of the dangers of Bitcoin.

"Really, what consumers need to worry about," Boyd said, "is just losing their investment. If you want to invest in Bitcoin, you just have to be comfortable in knowing you could lose everything you invested."

Another concern is the currency is used on the dark web.

"Normal banking institutions might have a safety and more secure way to store your money," Boyd said.

Craig, a proponent of Bitcoin said, "Yes, people on the dark web can potentially steal your money, but before the digital currency, they could steal your U.S. dollars."

He produced a documentary on living on Bitcoin for 100 days.

You can view it here: