illustration vs artwork

illustration and artwork both are nouns.

Word	Noun	Adjective	Verb	Adverb
illustration	Yes	No	No	No
artwork	Yes	No	No	No

As nouns, artwork is a hypernym of illustration; that is, artwork is a word with a broader meaning than illustration:

illustration: artwork that helps make something clear or attractive
artwork: photographs or other visual representations in a printed publication

Other hypernyms of illustration include art, graphics, nontextual matter.

illustration (noun)	artwork (noun)
a visual representation (a picture or diagram) that is used to make some subject more pleasing or easier to understand	photographs or other visual representations in a printed publication
an item of information that is typical of a class or group
artwork that helps make something clear or attractive
showing by example