If the device is set to backup to iTunes and the user has not selected the option to prevent automatic syncing when iDevices are connect, a backup is done automatically as part of the sync process.
That does not change the fact that the iPhone is designed for the user to regularly copy pictures and videos taken with the device off to a computer for safe keeping.
If a more recent backup exists, restore from it.
If one does not exist and the iPhone has not been used as designed, the pictures are likely gone. The only option left would be PhotoStream, if the user has enabled it.