Even though podcasting is usually an audio-only experience, attractive images can enhance your podcast branding and help you promote your podcast better! Here are suggestions to consider for podcast-level and episode-level images.
How images help your podcast
Establishing and reinforcing visual branding
Are Disney's movies Frozen and Frozen II related to Pixar's movie Onward?
Many of the 5by5 podcast network's cover art shares the same style, making the relationship obvious.
Marketing your episodes
Artwork makes your podcast look a lot better when shared in social networks like Facebook, Twitter, or LinkedIn.
Having images, especially for each episode, can help enable you to promote your podcast in visual-only platforms, like Pinterest and Instagram.