Where did you backup the photos to?
If you have been backing up your iPhone to iCloud or iTunes, deleting photos, taking more photos, backing up, deleting photos, etc. then there may well be no or very few photos in your most recent backup. When you delete photos from your iPhone they will not be present in the next backup. A backup reflects the current state of the iPhone when the backup is taken. Backups are not archives.
if you were backing up to your PC why can't you access the photos there?