iPhone 3G photos lost after update to 4.2.1 firmware

Hi, I recently synced my mums iPhone 3G to my Mac laptop. It hasnt been synced or backed up for a while as she lives far from me and doesnt have a computer.
iTunes said that it needed a firmware update so I clicked OK and it installed the new firmware. When the phone restored from the back-up created during the update, the photos (all 750 of them!!) were gone. I had not imported them yet as the update was running. Why were these photos not backed-up during the update?? Is there anyway to get these photos back?
iPhone 3G iOS 4 MAC laptop (not sure what software)