I am trying to publish a book which contains adult material

In addition to your drivers license, you need to keep production records of when the photographs were produced, when the book was/is produced, any other names you have ever used, and a variety of other things.  Section 2257 and the related regulations in the Code of Federal Regulations are record keeping requirements, not requirements that depicted persons be over 18.  That requirement is in other laws prohibiting child pornography.  If you keep the records required by section 2257 and the C.F.R.s, you cannot be successfully prosecuted under THAT set of laws and regulations.  If there is anyone else in any of the pictures you have to keep the records on them too, of course.  If you keep all these records and they are true and accurate in showing you were over 18 at the time the pictures were taken, that should also be a good defense if you were charged with child pornography too.  I'm not sure how a prosecutor could refute that evidence if, as I said, it is true and complete.

You right to publish a book such as this is protected under the First Amendment of the State and Federal Constitution.  States may pass laws to restrict just about anyone to publish a book but the statute must pass a strict scrutiny standard becasue this involves speech.  The statute in question is likely a valid statute that you must comply with as states do not want people under the age of 18 publishing adult matarial.  In this case, the burden is on you to comply with the statute.  If you were 18 when the pictures were taken and are 18 or older at this point in time, then you should obtain a certfied copy of your birth certificate from the town hall of where you were born and make a copy of your driver's license as these are valid to prove your age in the event you are questioned