From the support document, key words highlighted.
iTunes backups
From your Mac or PC, you can make a backup of your device in iTunes. Syncing your device with your computer isn't the same as making a backup. An iTunes backup includes nearly all of your device's data and settings. An iTunes backup doesn't include:
- Content from the iTunes and App Stores, or PDFs downloaded directly to Apple Books
- Content synced from iTunes, like imported MP3s or CDs, videos, books, and photos
- Data already stored in iCloud, like iCloud Photos, iMessages, and text (SMS) and multimedia (MMS) messages
etc.
If the photos are in the camera roll then they will be restored if you restore the backup. If they are in iCloud (an umbrella term for a number of features), or were uploaded from your computer they won't be. Extracting from the backup is possible but not straightforward. It would be better to make local copies either way. I say this having read multiple posts from users who found themselves unable to restore a backup when the time came. It doesn't happen often, but archiving your backups, spreading the risk with an additional backup to iCloud, and copying off all important data should be standard practice to minimise the chance of data loss.
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