If you found pictures that aren't yours, there's a good chance that they were shared from apps such as WhatsApp or Messenger. Most messaging apps save shared images and screenshots under the Pictures folder on your internal memory or SD card.

You can remove these pictures from Degoo by removing the WhatsApp or Messenger folders from your backup.
  1.  Open Degoo
  2.  Tap the menu button (on devices with small screens only)
  3.  Select "My files"
  4.  Navigate to your "Pictures" folder
  5.  Tap the three vertical dots on the WhatsApp or Messenger folder
  6.  Select "Delete"