@Commsman
It's not straight light that =)
Please there's some threads about cover that peoples explain detailed the process.
If you want to user your covers you need to make sure of some details :

Folder is in :

/home/user/.canola/covers

Inside is by

/artist/albumname

But there's a couple of rules( no spaces, no special characteres, etc)

And then.. you have 2 sizes of file:

300x300 and 150x150 (we use it to avoid rescaling hundreds of covers in the album screen)

and the name is cover-1.jpg and so on.

My advice would be : use Canola-tuning, it will create the folders for you download some covers that you may not want.. then you just move the good ones of you =)

Br

Marcelo