By default amarok saves all the downloaded album covers in “/root/.kde/share/apps/amarok/albumcovers” but if u re install your linux then all the covers are lost, and also if you use an external drive to keep music files and want to play these files in different computers and you will have to download covers on each computers.

Solution For this problem is using Copy Cover script of amarok  from http://www.kde-apps.org/content/show.php?content=22517 or directly download this from script manager of amarok (from tools menu) and use Get More Scripts. From here you can also get many more useful scripts like ( script to play video from amarok, display song name in pidgin and many more… )