AMG has the following song titles listed in its database (not counting a couple of obvious typos):

You Can't Judge a Book
You Can't Judge a Book by Its Cover
You Can't Judge a Book by Its Hair
You Can't Judge a Book by Looking at the Cover
You Can't Judge a Book by the Cover
You Can't Judge the Book
You Can't Judge the Book Polka
You Can't Tell a Book by the Cover

Willie Dixon is most often credited as the author, but Rick Springfield does a version that he claims authorship for himself. But even when Dixon is credited, the titles aren't consistent.

I think "You Can't Judge a Book by Its Cover" is most likely the correct original title, based on the fact that Chess Records uses that title in the compilation, "The Chess Box."

The one written by Willie Dixon has been recorded by Bo Diddley, the Yardbirds, the Fabulous Thunderbirds, Tim Hardin, Sleepy LaBeef, Eric Clapton, the Monkees, Hank Williams Jr., Patti Labelle, John Hammond Jr., Dion, Stephen King (yes, the writer, on "Stranger than Fiction"), and others.

Oddly, I could not find any evidence of a recording made by Willie Dixon himself.

It's not unusual, in the folk or blues field, to find variant titles, but it's unusual to find so many variants, especially when the author is known.

(I'm not related to him, by the way, although I did coincidentally name my son William.)