CryptoNote is the name of the application layer protocol of privacy coins like Monero and MoneroV. Not to be confused with the ⛏ Proof-of-Work mining algorithm CryptoNight.
Key images are derived from a private key and all users keep a list of all the used key images. If a duplicate key image is detected, the transaction gets automatically rejected, thus preventing double-spending. Until now there hasn't been proof of any double-spending attack in the history of CryptoNote.
CryptoNote's proof-of-work algorithm CryptoNight allows for fairer hashrate distribution among individual miners and ensures smooth coin emission. CryptoNight is also ASIC resistant which naturally creates a vibrant community of mining pools, thus reducing the risk of a 51% attack.
No, because CryptoNoteCoin was just created as a showcase of the technology with zero commercial value, the genesis block gets replaced every 2 months, making it worthless.
Bytecoin was the first, their team worked closely in cooperation with the CryptoNote Team to release it back in July 2012. Monero is a fork from Bytecoin and MoneroV is a fork from Monero.
While blockchain moves on to bigger and more widespread uses, privacy will be more of concern than it already is. Cryptonote is the leading privacy protocol and more than ever, having the control over your own financial privacy is of paramount importance.
