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Casascius Bitcoins are a type of physical representation of Bitcoin that was first introduced in 2011 by Mike Caldwell, a Utah resident who is also a huge fan of the cryptocurrency. These coins were widely available until November 2013 when the US government intervened and called off the operation. What sets these physical bitcoins apart from others is that they contain redeemable BTC and have a private key hidden under a hologram layer imprinted on the coin.
Source: fullycrypto.com
