iPod touch general ipod question about updating album art

i dont have very much album art, since i never bothered to keep it before when i just had an ipod nano. but now with an ipod touch with coverflow, i want album art for all my music, but dont want to have to add it twice, in my itunes library and on my ipod. is there anyway i could just update the itunes library, and have it synch all the photos over to my ipod? i have it set to manually manage music, cuz i have way too many songs on my comp, so i wouldnt be able to just tell it to sync again. if i hit the sync button, will it update the songs already on my ipod, (since i have it set to manually manage it shouldnt add more songs)