Your cover art should follow the following guidelines:
JPG, PNG, or GIF image file
Smaller than 10MB
A perfect square and at least 1600 x 1600 pixels. iTunes recommends images to be 3000 x 3000 pixels )
Best-quality RGB Color mode (including black and white images)
Resolution of at least 72 dpi (300 dpi is better)
Images that you own the rights to distribute
*Failure to adhere to these requirements may result in your song being rejected by some stores.