That was the point of my last sentence: metadata exists for honest people who choose to do the right thing. Anyone dishonest can trivially strip this but the snake-oil vendors like digimark only raise that bar enough to catch the most inept thieves.

Put another way: Buzzfeed could trivially put a system into place to scan images to prevent mistakes. It would be a much harder problem to reliably stop dishonest editors – at that point, it'd be better to simply use something like TinEye or Google Image Search.