I'm glad you are interested about editing your playlist images.
Currently this option is available only for Spotify, labels and other commercial accounts (like playlist sharing services). They can also add a text/links to playlist. Only image change system is currently also available for most super users here in Community. Text can be added if superusers contact Spotify. Sadly currently this option is no in use in other accounts.
@rdmfitness This is something I would love to see introduced for all users as well. The only way you can currently achieve this (that I know of) is to join the Community Rock Star program (2 links below) and get active in the community to become a Rock Star. Once you have this status, you can preview new features before anyone else, including custom artwork for your playlists.
sadly, i dont think personal playlist covers are for all accounts but i do think the rockstar account application would be worth a shot filling out & you might be able to unlock that feature. google doc link : *Link Removed.*
I have heard of this being possible with the new Spotify update on Windows. It's a different version that iOS/Android hasn't released yet. Hopefully they will soon! I'd love to be able to add a custom pictures for my playlists. Aside from this, what you can do now is pick 4 album covers you like, and drag them to the top of your playlist to create an "art" look. Hopefully this helps!