Checked the specs for podcast from apple, the image tag or itunes:image look only for the cover page for itunes store. Set it, I still can’t see pictures.
After 50 times re-tries, I suddenly realized that the image I’m looking for is called artwork of mp3, it’s not set by podcast feed at all, it’s right in the mp3 file!!!
Scott H got the solution how to encode images into mp3. But for my case I need it running on linux.
Had to using eyeD3 to upgrade idtag to v2.3 before add cover image for itunes display purpose.
Putty is way better than the sshclient I was using. Stable, copy&paste support, and even more, colorful console!