One very important thing when it comes to music distribution is the cover image. If a band’s not into the graphic design or photo business, they should not try to make it themselves. I have seen intentions to use cover images for the upcoming release made in paint. I have also seen no artwork at all, just because the band didn’t know how to find one that could help them make it. (Maybe they thought it would magically pop out from the blue and make it to the release date, I don’t know)
However, these are the requirements/limitations you need to start from for a digital release:
Filetype: JPG or GIF
Geometry: Perfect square
Size: At least 1600 x 1600 pixels in size
Quality: Best quality RGB Color Mode (this includes black and white images)
Note: If you’re distributing your music to the Amazon (for printing physical CDs), you need a resolution of 300 DPI.