bliss embeds album art into the music files themselves. iTunes has to be told about the new album art. In iTunes, right click the album affected, click 'Get Info' and then click 'OK' on the next window. This forces iTunes to retrieve the album art from the music files, and use it in iTunes. If you need to do this for many albums, try multi selecting the albums concerned.
Any other FAQs I forgot or clarifications required? Post your ideas below!