Yes, you can permanently delete individual photos and videos, and even entire inspections, whether in-progress or completed.
You can archive properties (along with their associated data) that you no longer manage in order to remove them from your active inspectable property list but preserve the data for future reference.
You can even delete properties (along with their associated data) that you have no need to preserve.  zInspector will not retain your data if you choose to delete it.