Some Kindles will let you display the cover of what you're reading on the lockscreen

Amazon has finally realized some people want to show off what they're reading at the moment. And so, some Kindle models can now show the book cover of the title you're reading as your ereader's lockscreen paper. It's rolling out globally, and most books, magazines, comics, and manga are supported. As long as you have a non-ad device, Display Cover works on 8th and 10th generation Kindle, 7th and 10th gen Paperwhite, 8th to 10th gen Oasis, and 7th gen Voyage. You can check out if yours is compatible here. The feature is accessible through the Kindle's settings menu. Toggle the "Show Cover" option to activate it.

Source: Engadget