There are some specifications for the cover that Amazon asks. I will paste them here:
Kindle Direct Publishing currently accepts two types of files for cover images:
JPEG (JPEG / JPG)
TIFF (TIF / TIFF)
We apply additional compression to images when displaying them on the website. For best results, please upload your images with minimal compression.
Requirements for the size of your cover art must have an ideal height/width ratio of at least 8:5 (1.6), meaning:
• A minimum of 625 pixels on the shortest side and 1000 pixels on the longest side
• For best quality, your image should be 2500 pixels on the longest side
Important: We cannot accept any images larger than 10,000 pixels on the longest side.
Your cover image must be less than 50MB. If the file type you are using supports compression, make sure to enable as little compression as possible, e.g. none for TIFF. Be sure to save your file with 72 dots per inch (DPI).
Product images display on the Amazon website using the RGB (red, green, blue) color mode or profile. RGB is the color mode native to the web and many color screen displays, as these three colors displayed at varying levels of intensity create over 16 million colors. When saving and uploading your cover image file, save your file ONLY as RGB - not CMYK or sRGB- for the color profile. You can usually find this option in the File saving dialog of image manipulation programs such as Photoshop.
Some programs may also refer to RGB color as 'True Color' in some programs. If in doubt, try opening a JPG inside Internet Explorer, Firefox, or Safari. If a JPG opens fine inside a web browser, it's most likely okay to use as a cover image.
Make sure to save your image without color separation. This is usually a pre-press or color palette option. Use your image manipulation program or image analysis tool (some are available free online) to verify that your image file doesn't have color separation.
Use color images whenever possible and relevant.
Borders for White Cover Art
Cover art with white or very light backgrounds can seem to disappear against the white background. Adding a very narrow (3-4 pixel) border in medium gray will define the boundaries of the cover.