Is there an free software for Mac which can get you high quality album art?

Many songs in my iTunes are from CDs and iTunes couldn't find artwork. So I decided to manually go through and add my own artwork, however that picture, when played on my iPhone (which is the only device I play music on), is very blurry. Is there a software that can scan your library and find high quality album artwork to replace with ones that are missing, not matching, or low quality?

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