In your marketplace, from the Admin panel in the Design tab, you can configure two cover photos.

You can find resources about great photos in this article.

The cover photo is shown in the homepage for non-signed-in users.

That photo should be 1920x450 pixel size. The file should be a jpg, png, or gif.

If the photo you upload isn't 1920x450 pixel size, it will be resized automatically and taller images will be cut in the middle (top and bottom will be cropped).

To enjoy the best results, you should use the recommended size.

The cover photo is shown in all pages except in the homepage for non-signed-in users. A light grey/white overlay is applied and the search bar is added on top of that photo.

That photo should be 1920x96 pixel size. The file should be a jpg, png or gif.

If the photo you upload isn't 1920x96 pixel size, it will be resized automatically and taller images will be cut in the middle (top and bottom will be cropped).

To enjoy the best results, you should use the recommended size.

You can use a basic image editor (like Paint) or some online tools like Cropp.me or Cut My Pic.