Which comes first - the cover or the title?

Cover reveals are an important event in the life of a book - the first time it gets to appear on the world's stage. A cover sums up the contents of the book, so it's quite exciting. But I have been wondering lately about the relationship between cover and title. On a paperback book the way it looks on the shelf is probably more important, but with e-books? I know that a cover is meant to look good as a thumb nail - but a thumb nail is a very small area. Can you really make out too much detail, except for the colours? 

And such a lot of covers look rather like each other. Thrillers with a indistinct but colourful background and the title in large letters, often with a strap line as well, or even more than one. The title - words, being the thing that stands out. And all those historicals with an interchangable, partly dressed heroine in a succession of pretty, colourful gowns. It really can be difficult telling one from another.  And the cookery and self help books with the picture of the chef or the guru. And the thrillers that are all about some sort of quest, that have a vaguely historical looking scene, often with the back view of a figure in it. Sometime running. And sagas with a group of girls or a group of children or one child, looking woebegone in period costume. And the drawing of a cottage on a village green for romantic comedy. And snow scenes at Christmas and beach scenes for holiday reading. And we won't mention all those guys who have managed to lose their shirt somewhere along the way. All those covers do their job - they immediately tell you what the genre is - but it seems to me that lately it's the title that makes the difference.  Which is rather gratifying, because a title is words, and books are about words. 

But,of course, the author often doesn't get to choose the title ...