After 20 years in suspended animation copyrights have expired on works created in 1923. Congress, bowing to pressure from a few corporations, extended U. S. copyright rights from 75 years to 95 years in 1998. Some details of the results can be read here and here and here.
Some creations never had their copyrights renewed under the old laws and have entered public domain long ago, others kept on top of it and retained copyright. Those wanting to use earlier works had to slog through incomplete copyright records and then take the chance of a suit if they erred.
But now works created before 1978 have a maximum copyright expiration date of 95 years. (Without change the first Mickey Mouse will be public domain in 2024.)
So now all comics from 1923 are available, though trademark rules may still apply.
That would include the 1923 strips of Krazy Kat, Mutt and Jeff, Katzenjammer Kids, Slim Jim and the Force, anything from 1923 (or before) by Opper or McCay or Goldberg, and hundreds more.
That said, here are some strips that began in 1923:
Moon Mullins began in 1923. Yes, it ran the full width of a newspaper page –
and they weren’t the skinny 11 inch wide pages of today’s papers.
Percy L. Crosby’s masterpiece Skippy first appeared in March, 1923 issues of Life.
The animated Felix the Cat was introduced to the public in 1919, in 1923 came the comic strip.
But a word of warning.
You can’t just take,say, the Walt and Skeezix 1923-1924 book from Drawn & Quarterly and reprint the 1923 strips. That collection is copyrighted. You gotta go find the strips yourself.
However you can reprint the inside contents of a 1923 Barney Google collection,
but you would have to change the cover. Barney Google and Spark Plug are still trademarked
by King Features, and who knows about Cupples and Leon?
I’m a fan not a lawyer, you probably want to see one before trying anything.