Backingup

It depends on whether or not the photos are already stored in iCloud (via iCloud Photo Library, etc). If they are, then they are not included in a backup. See the following for complete details: About backups for iOS devices - Apple Support

Whether doing an iCloud or iTunes backup, the only photos ever backed up just those in the camera roll folder. Similarly, things like contacts are expected to be sync’d from somewhere (e.g. iCloud) so are not part of a backup.

What does iCloud back up? - Apple Support