[Related: Distorted Videos of Nancy Pelosi Spread on Facebook and Twitter, Helped by Trump]

Digital technology is making it much easier to fabricate convincing fakes. The video that Mr. Brooks created is pretty simple; you could probably do it yourself after watching a few YouTube clips about video editing. But more complicated fabrications, sometimes called “deepfakes,” use algorithmic techniques to depict people doing things they’ve never done — not just slowing them down or changing the pitch of their voice, but making them appear to say things that they’ve never said at all. A recent research article suggested a technique to generate full-body animations, which could effectively make digital action figures of any famous person.

So far, this technology doesn’t seem to have been used in American politics , though it may have played some role in a political crisis in Gabon earlier this year. But it’s clear that current arguments about fake news are only a taste of what will happen when sounds and images, not just words, are open to manipulation by anyone with a decent computer.

Combine this point with an insight from epistemology — the branch of philosophy dealing with knowledge — and you’ll see why the Daily Beast was right to expose the creator of the fake video of Ms. Pelosi. Contemporary philosophers rank different types of evidence according to their reliability: How much confidence, they ask, can we reasonably have in a belief when it is supported by such-and-such information?

We ordinarily tend to think that perception — the evidence of your eyes and ears — provides pretty strong justification. If you see something with your own eyes, you should probably believe it. By comparison, the claims that other people make — which philosophers call “testimony” — provide some justification, but usually not quite as much as perception. Sometimes, of course, your senses can deceive you, but that’s less likely than other people deceiving you.

Until recently, video evidence functioned more or less like perception. Most of the time, you could trust that a camera captured roughly what you would have seen with your own eyes. So if you trust your own perception, you have nearly as much reason to trust the video. We all know that Hollywood studios, with enormous amounts of time and money, can use CGI to depict almost anything, but what are the odds that a random internet video came from Hollywood?