All album artwork gone on iPhone, aside from iTunes purchases?

I just noticed a mess-up in a song name, so, while I had my phone synced, I deleted the item on my phone, from the "on my device" tab on iTunes. I proceeded to add the correct version of the song onto my iPhone, and after doing that, along with the new song, it synced 27 songs which I had recently deleted. I then went to my music on my phone, and found that the entirety of my album artwork for songs that were not purchased on iTunes had been deleted! I resynced my phone multiple times, quit iTunes and reopened, quit the music app, and restated my phone; none of which worked. This is really getting on my nerves, and any light shed on this issue would be much appreciated.

You deleted non apple purchased music… You lost the art work.( the file that has the art work for each song )… Soo-o-o-o all you can do is… Redownload those songs…