Omitting photos when backing up an iphone to a macbook with itunes I have a 64GB iPhone 6 and a MacBook Air with a 256GB disk, about 20GB of which is empty.  There are about 24GB of photos and videos on the iPhone, all of which have been imported into the Photos app on my MacBook. Thus I have a backup of the phone photos on the MacBook.  But when I try to sync my iPhone to the MacBook through iTunes, it tries to copy all the photos into the backup and fails because there is not sufficient free space on the MacBook disk.  Since I already have a copy of all the photos in the Photos app., there is in fact no point in iTunes creating a second copy during the backup.  But everything else on the iPhone should be backed up.  

Thus what I need is a way of telling iTines to backup everything on the iPhone except the photos.  However, I cannot find any way to do this (apparently rather simple) thing.  is it possible, or is there some work around?
I am assuming you are not using iCloud Photo Library, but are importing the photos into Photos through a USB cable.

What you can do is remove the photos from the iPhone after importing them, and then sync them to the iPhone through iTunes. As far as I know, when not using iCloud Photo Library, an iTunes backup of an iPhone will include a copy of all the photos in the Camera Roll of the iPhone, but it will not include another copy of all the photos that were synced onto the iPhone through iTunes (Apple Support states that “An iTunes backup doesn't include: [...] Content synced from iTunes, like imported MP3s or CDs, videos, books, and photos”). This way you can still view the photos on your iPhone without having two copies of them on your Mac.