SHARE When a single work of digital art, which will never hang on a physical wall, sells for $69 million at a Christie’s auction in March, or a picture of a routine column from a tech writer for the New York Times, which could be read online for free, is bought for an astounding $560,000, some perspective is desperately needed. These prices were commanded in recent weeks as part of a current craze over nonfungible tokens or NFTs. The digital-only elements, existing solely on a vast network of computers that control the blockchain, have actually been around for several years. But when tens of millions of dollars are suddenly tossed around for something that only exists in cyberspace, it’s clear that a lot of people are taking a renewed interest in the evolving world of digital currencies.