I flew yesterday, and arrived early enough to watch the crew get onto the plane. There was a cursory check of their IDs, but very cursory. The main thing seemed to be that everyone knew each other; the crew had worked together before, and the flight agent who checked their IDs knew them. I would not be surprised if the flight agent was given pictures of the pilots as well as their names, though, which would probably provide the greatest security (identity verified by a trusted third party, the airline, without any chance for the pilot to interact with the verifying document, as happens with passports or other ids. If you never get to see it, you can't tamper with it).