ITunes artwork sync to iPhone?

I just downloaded a mix tape and imported it into iTunes. For some reason it didn't sync the artwork. So I put it in manually. All that went fine. However I just synced the mix tape into my iPhone & the artwork isn't there. I've deleted it then synced quite a few times but no luck. Any advice?

That happens to me sometimes when I can't add artwork at all I normally convert a track to MP3 or AAC or something and put the artwork in the converted tracks and sync them to my iphone that works for me hope it works for you to