When you connected your iPad to iTunes, you will came across  "photo" in the menu on the right side of itunes once you select your iPad. Choose your desire photo location(for example a "my photo" folder in your D drive), then you will have an option to choose "all folder" or "selected folder". Whenever you need to transfer your new photo into your iPad, copy them into a new folder and put it into the"my photo" folder which you choose from your iTunes. The first time will take some time(if you have a lot of photo to sync) but if you adding new photo again with the same process, iTunes will detect your previous photo and only sync your new added photo into your iPad.

I think TS misunderstood what "sync" means.

Sync means it will keep both ipad and your pc/mac the same. So if you delete stuff from the sync folder on your pc, the sync software will think that you want to delete those stuff from your ipad as well. To keep the old photos in your ipad, don't delete them from your sync folder.