Just been sorting out album art for my MP3s on my SD card as a few albums weren't showing the picture so I thought I'd share my findings. As per this post I was able to use 800 x 800 album art successfully: 

 

Certainly the few files I had with album art over 1000 x 1000 pixels didn't work so I resized them to 800 x 800 using the "Sanse MP3 Art Sizer" tool and the album art now appears.

 

This really should not be a problem. It's a bit disappointing from Skoda.

Thanks for the info.

I might have to get hold of a windows machine to fix this at some point. Most of mine are ok, so motivation low. :-)