The URL in your 'itunes:image' tag is
http://i67.tinypic.com/2hdsm7m.jpg
This is not an image, but redirects to
http://tinypic.com/view.php?pic=2hdsm7m&s=9#.Wi6tIRTAVtU
which is a web page which includes your image. This won't do: you must provide a direct link to the actual image. TinyPic provide a supposed 'direct link for layouts' but the URL there leads straight back to the web page. It rather looks as if you should find somwhere else to host the image.
You do have a direct link to an image in your 'image' tag (which iTunes does not read):
yt3.ggpht.com/-ktMNoG9FSY0/AAAAAAAAAAI/AAAAAAAAAAA/wmG8_aVxJXA/s240-c-k-no-mo-rj -c0xffffff/photo.jpg
(I removed the http:// because otherwise the forum software will truncate it). However this is 240 by 240 px and so isn't acceptable.
The image itself must be minimum 1400 x 1400 px, maximum 3000 x 3000 px (there's no point in going that large, though), JPG or PNG, RGB, and must be less than 500kB.
You have a different image in the 'itunes:image' tag for each episode, however these do not appear on your Store page. The one for episode 5 is https://i.ytimg.com/vi/UtEq45viGwQ/maxresdefault.jpg and is 1280 x 720 px - it should be square.
You have made use of the 'itunes:order' tag, but this has resulted in Episode 5, the latest, being numbered '0' and then episodes 4,3,2,1 being numbered 1,2,3,4. This is going to result in your having to renumber all these tags every time you add an episode. You don't need it anyway: the Store and iTunes itself will display episodes in reverse order - latest on top - anyway, unless a different order is specified, which you presumably don't want. I should just remove these tags.
