Can't sync photos from Windows to iPhone since iOS 6
Alright, I got it working again.  Something in the following ritual did the trick:


remove all photos and videos from the sync directory on the Windows system
sync
empty out the directories on the iPhone visible through the windows explorer
remove all photos and videos from the iPhone
sync
recreate the sync directory on the Windows system with all the directories and photos (except the "Thumbnails" folder) as you want them
go back into iTunes while the iPhone is connected, note that the "sync photos" checkboxk is cleaerd, re-check and verify that iTunes is looking at the correct sync directory
sync


...and the photos are there.  I don't know which chicken-wave was the one which actually fixed the problem.