I seem to be having the same issue as a lot of people trying to get there podcast up on i Tunes.
There are definitely benefits to using i Tunes Connect, and we’re excited to see what other tools Apple launches for podcasters.
(Problem art may also be accompanied by questionable Certificates of Authenticity.
To evaluate a Certificate of Authenticity or COA, read Is Your Certificate of Authenticity Worth the Paper It's Printed On?
Furthermore, i Tunes doesn't validate the feed nor the image.
At any point in a work of art's history, it's authenticity can come into question.