Before long, the new designer had an actual design job. Today, some 15 years later, Mendelsund's an associate art director at Knopf, having designed around 600 covers.

A TikTok user, who goes by the name Kelly on the social media platform, has re-created a mock-up of Prince Harry’s book cover that was parodied on a recent episode of South Park.

But lately, another cover design trend has been popping up on this summer’s crop of beach reads: the flat woman. Inspired by the “ flat design ” that’s become standard on the Web, these ...