I think the first order of business is look at the top performing images related to your genre. A little benchmarking research should take you about 10 minutes. See what their patterns are. Then beat them.
Personally I would have a page that has two or three different versions of your cover art available for download so you could have the largest highest quality image and then create them for specific social media outlets if you want people to download them and have that on a page for each cover art.
Link to the actual audio or video file as well. You might even have them on the same page and then if you post them to YouTube have links on YouTube to download the cover art etc.
As far as alt tags when you do this strategy they will matter less because Google understand what the images are a lot more when you have separate pages for them or included in the actual audio files.
Erotic hypnosis for women cover art 3000×1500
Erotic hypnosis for women cover art for Facebook (whatever the dimensions are)
Erotic hypnosis for women cover art for Instagram (whatever the dimensions are)
These are the most obvious, I think.
You could include things like
erotic sexy cover art for men
Etc