For the stores to accept your artwork it must be:
A JPG/JPEG/PNG file
A perfect square, ratio 1:1
At least 2800 x 2800 pixels, but we recommend 2800 x 2800
A large, high quality image
If you need to re-size your artwork and are not sure how, we recommend using picresize.com. It’s free and very easy to use on both PC and Mac. Go to the site and follow the steps to create your square image.
Please make sure you also read the artwork requirements and guidelines to ensure your release is not rejected.