When it comes to media-related RSS, basically podcasts and music, iTunes is a big player, so big, that some media platforms ensure to be compatible with iTunes’ RSS more than with W3C’s RSS. In practice, RSS Polling works just fine with these feeds, excepts that it doesn’t recognize the syntax for images. It looks like this:
Some RSS services / apps will be adapted to recognize this syntax and show an image. For instance, I have tested this with https://antennapod.org/ . It would be great if RSS Polling could recognize this syntax and poll the images as well.