Album art is not shown

[capponz]

Hi, most of my files are ogg files (maybe that could be a reason).
I grabbed all the related album art with n7player which is able to ID3tag the album art to the files.
Unfortunately Neutron does not show most of the album art.
even after re scanning, deleting and re setting up the folder source.
is there any known fix for that? any ideas?

every point into the right direction is highly appreciated
thanks