This piece by Norman Rockwell, for example, is given credence as “actual art”, while his Saturday Evening Post covers are not.
I think that’s pretty much it, although I’d add that an illustration or other work of commercial art can be less obvious or “on the nose”…but this depends on the nature of the assignment as well as the talent of the illustrator.
Looking at previous featured artists on the site I linked to before, I liked Sarah Brannen’s “Night Street” a lot. The first picture of hers, “Field Mouse Thanksgiving” is very cute and I’d guess technically more difficult than “Night Street”, but it doesn’t say much to me other than “here’s some cute mice eating corn”. “Night Street” strikes me as being more evocative and far more interesting. In the context of whatever book it’s an illustration for it’s probably clear what’s going on, but taken alone there’s some mystery about the figure and its purpose. It’s not a Vermeer or anything, but I’d hang it on my wall. “Field Mouse Thanksgiving” is more the sort of picture I’d want on a holiday card to send to my mom. Yet both are illustrations painted by the same person.
“Blow me” is not appropriate for Cafe Society, Koxinga. Save that for the Pit.
Yeah, sorry. Mistyped.
To make it easier: File:Hockney, A Bigger Splash.jpg - Wikipedia
Now, try NOT to imagine that as cover art for the next Chili Palmer book.