To begin with Things, we see about any Facebook record is their Profile Picture, If you Find any Facebook Account on your Friend list suspicious, First thing you will do is Use Reverse Image Search.(This simply means scanning the pic on Google images)

 This helps you see whether Similar Pictures are accessible on Internet. To start with, Download the Profile Picture of the record you find suspicious

Go to Google images(www.Google images.com) Click on Camera icon which says Search by image, Click on Upload an Image, now choose the Picture you  had downloaded earlier , Now once the uploading Completes, google will show you Similar Images that already exist over internet.


so simple