Album Artwork Problems

So I've been slowly working on gathering album artwork for all of my albums in iTunes. I tried the "Get album artwork" feature in iTunes but that usually gives me horrible quality artwork or it won't find it at all. So I've done it manually by selecting the album, then dragging the artwork into its appropriate box. The only problem is that when I transfer the songs from iTunes onto my iPod the artwork doesnt show up on the iPod? Although when I go back and check if it has the artwork in iTunes it will be there. Any suggestions? I also want to know how to completely remove ALL album artwork in iTunes. I've tried selecting all songs then File>Get Info .. then I just click the box next to album and hit OK. Shouldn't this work? The only way it works for me is if I manually go and do it to EVERY song individually. Sorry if this is confusing to read hahaha. Any help or ideas are appreciated.

-Keef.