Upload automatically generates an image from your podcast's cover art:
Example of automatically generated static image
If you would like to use your own image, you can upload one by going to the podcast you want to edit, click the Settings tab, scroll to Video preferences, click Use your own image, and then upload an image file. Currently, you can only upload a PNG, JPG or JPEG image. Although it is not required, it is recommended you upload a high quality image with a 16:9 ratio, so it displays well on video platforms in landscape mode.
Screenshot of the Video preferences section in podcast settings
If your podcast host supports uploading images for individual episodes, you can override your settings and use that image instead. Go to the podcast you want to edit, click the Settings tab, scroll to Video preferences, and select Prioritize episode-specific image.