As you probably know, when the rights for a writer's hard-cover or paperback book revert to the writer, the rights to the nice cover the publisher had their artists design for the book do not revert. The writer must make or hire another cover for the e-book. And there's a lot to think about, when you do this. You know how it is with covers. They should be thematically related to what is written in the book, attention-getting, and attractive. Legible is also good.
Do a search online for good book covers and the internet will show you artistic covers from the golden age of publishing. THE GODFATHER. THE GREAT GATSBY. Stuff like that.
I like Hank Phillipi Ryan's cover for THE OTHER WOMAN. Red, white, and gray are perfect colors for a political thriller, and the bridge and the woman in the red coat have to do with what the book is actually about.
Inspired by this, I got busy and made new covers for UNBALANCED ACCOUNTS and THE DEATH TAPE, the first two books about soft-boiled Trenton detective Nick Magaracz. Do you like them? Would they get you to buy the book? I think I like them. They're kind of arty. Maybe a little grim, but we aren't dealing with cozies here. The pictures are real pictures of Trenton. I tell you what, though, if I thought it would sell books I'd put LOL cats on the cover.