Your podcast cover art is the square image that listeners see on their listening devices and on most podcast players.
Each podcast can have a couple of types of artwork:
Podcast show artwork - the cover art for the podcast itself, the main cover; and
Podcast episode artwork - cover art specific to each episode, shown in more and more podcast players on an episode-by-episode basis
Luckily, both pieces of artwork follow the same specification.
Note: With the release of iOS 17 and support for individual episode artwork, Apple Podcasts has changed the requirements for podcast artwork. These specifications are below.
A square image
3000 x 3000 pixels in size
JPEG or PNG format
Max 1MB in file size (JPEGs are smaller in file size)
From experience, don't put anything naughty on the artwork, either. They won't like that. That means:
No swearing or explicit language
No explicit images
No offensive or discriminatory imagery