If your artwork is not between these image requirements, you will receive an error from iTunes that says “Podcast cover art must be at least 1400 X 1400 pixel JPG or PNG, in RGB color space, and hosted on a server that allows HTTP head requests”.
Checking your artwork's pixel dimensionsFind the file size and pixel dimension of a file from a saved file on your computer, or through your RSS feed.
Saved file on your computerIf you have the image saved on your computer, you can find out the pixel dimensions through the image’s information.
On a Mac: Open the image file in Preview. Click on Tools in the top menu and select Show Inspector. A pop-up window will open, and under the title ‘Image size’ you will see the pixel height and width of your image.
On a PC: Right click on the image file, look at Properties, and then the Summary tab.
Your RSS feedIf you are unsure what dimensions your artwork is, go to your RSS feed (Available through your Content Settings page) and copy-paste the link within the <itunes:image> tag like this:
From there, open up your console, and scroll over the img style tag to view the pixel dimensions of your artwork.