What Makes Podcast Cover Art Great
The first and most obviously key to successful podcast cover art is to meet all of the iTunes standards. The minimum dimensions for cover art to upload to iTunes is 1400 pixels by 1400 pixels while the maximum image size is 3000px by 3000px. I strongly recommend designing and uploading at the maximum allowable size to help future-proof your cover art. Digital displays continue to grow in both size and pixel density; things like 4k monitors and Apple's retina display are just the latest iteration in an ongoing trend. Uploading at the maximum allowable resolution will help you stay ahead of this curve as much as possible. It is worth considering a vector-based design for your cover art because vector graphics can be infinitely resized with no loss of quality.
RGB images are the only type allowed in iTunes, which is fine because you shouldn't be designing in CMYK, grayscale or anything else when the digital world is the primary destination of your work. Just make sure to double-check the color mode as soon as you create a new document; if you have to change color modes halfway through creating your design, there may be unwanted color shifts in your file.
iTunes only allows jpg or png files to be uploaded, so you will need to export you design in one of these formats. Jpg is the most common filetype to use as it is generally smaller and handles photos and other images with a lot of color and gradients better than a png will. If your cover design only contains a few colors and doesn't have many gradients, like my Rich Tips design, a png file may be a better option. If you're not sure which to use for your design, just try both options and see which one looks better. If both filetypes look great, choose the one with the smaller file size.
iTunes Content Rules
You cannot use trademarks that you do not own or have permission to use in your cover art. This not only includes third-party trademarks, but also Apple-related trademarks. Things like iTunes or the Apple logo and even Apple hardware (such as iPhones) are off-limits.
Avoid obscene and offensive words and imagery. This one is a bit more subjective so I can't tell you exactly what you may be able to get away with, but I can give some examples of what to avoid. Don't include things such as illegal drugs, profanity and depictions of sex in your cover art. If you think your cover art may be questionable, my advice is pretty simple: better safe than sorry. There are always creative alternatives to get your message across without risking your upload being rejected or not considered for the "New and Noteworthy" section of iTunes.
Great cover art will be high-quality. I'm not necessarily talking from a stylistic standpoint, we'll get to that, but from a more technical angle. You don't want any jpeg artifacts or pixelation in your cover. Any photoshop cutouts or isolated objects need have nice, clean edges. This goes for text as well.
Acceptable to Good
So far, I've focussed on meeting the iTunes requirements for quality and content. None of this makes your cover art great, it just means you have something that won't be rejected by iTunes. If you're capable of uploading a podcast, there's a good chance that you would be able to hack something together in photoshop and meet this list of requirements. But if you're reading this site, you aren't interested in the bare minimum; you want the best freakin cover art you can get. Well, my friend, read on to find out what it takes to push your cover art from merely passable to something that is a strength of your brand.
Legibility is king when it comes to podcast covers. The various sizes that your design will be displayed at, especially the very small sizes, push readability to the top of you priority list. Choose fonts that maintain legibility at small sizes and make sure that the main text is large enough that it is reasonably sized even when the design is scaled down to a thumbnail.
Be sure that there is plenty of contrast between your text and the background. This means not just contrast in value and color, but the busyness of the background. A very complicated background photo can make it hard to discern the letterforms of the text.
One simple approach you can take that will have a huge impact on legibility is to limit the amount of words that you include in your design. Adding more text will force you to decrease the font size and create more visual chaos for the viewer to sort through. Only include what is necessary; this often means the title only. A tagline or the names of the show hosts can be included if they are not too long and are handled with care. You may have to accept that this secondary text will not be readable at the smallest sizes.
As I've been hinting at, you need your cover design to work at a variety of sizes. Don't get too hung up on testing your design at every possible viewing size; you would be trying to hit a moving target. Like I said, displays are always improving, iTunes can change it's layout or requirements at any time and people use a variety of different podcast apps and devices which show your art at different sizes. If your cover art looks good at 55px by 55px and 3000px by 3000px, you should be covered. If that's not specific enough for you: 1400px, 300px, 220px, and 125px are commonly used sizes that you could also test your design at.
Good to Great
So we've covered meeting iTunes requirements for cover art and what makes cover designs attractive and readable, but we're not done. As Ed Catmull said in his book Creativity Inc., "Ease is not the goal; excellence is." We can do better because we care and we're willing to put in the work.
So what sets great podcast cover art apart from technically sound, but ineffective designs? First, your cover art needs to communicate what your show is all about. This can mean the subject of the podcast or the attitude and mood it is presented in. Or, ideally, both. Podcast cover art should also be eye-catching to help draw in new listeners.
But that's not all. The mark of truly exceptional cover art is that it makes an emotional connection with the viewer. The mark of truly exceptional cover art is that it makes an emotional connection with the viewer. This connection draws new listeners in and helps build loyalty with your audience. If you can achieve that, you've done something really special for your podcast.