Photos lost when synched initially

How did the photos originally get onto the iPad ? If they were synced from a computer then they won't be included in a backup, so restoring to a backup won't copy them back. If they were not synced from a computer (e.g. they were taken with the iPad, copied to it via the camera connection kit, or saved from emails/websites) then had you taken a backup of the iPad, either to the cloud or to a computer's iTunes, after they were taken ? If you had then you can try restoring to that backup.

Backups and restores : iOS: Back up and restore your iOS device with iCloud or iTunes

If not then you could try doing a search for programs that claim to be able to recover content from a device (I hadn't tried any so I can't suggest one).

When you connected the iPad to that computer you replaced your existing content of the iPad with content from the computer's iTunes. If you hadn't taken a backup prior to doing that then you will have lost the photos, though you could try doing a search for programs that claim to be able to recover content