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Prove a video clip was recorded in continuous-time

  1. Dec 21, 2011 #1
    I am looking for an answer based on Logic and not necessarily a technical one.

    Suppose, if I have a video clip of me doing something (let's call it event 2: E2) and would like to convincingly prove to others that it happened after a certain date - say, 2011-01-01. One rather simplistic idea would be to do E2 while standing next to a TV show/news showing an event E1 that has happened only once, ever, on 2011-01-02. This would prove that E2 happened after E1 and therefore after 2011-01-01. I know you can completely disprove this idea by faking it using a video older than 2011-01-01 and superimposing a very recent TV shot. For the sake of the problem, assume we can guarantee using some technical solution that the video was not edited since the time it was saved by the camera.

    My Question is: Using a similar reasoning, can you prove that a video clip was shot in continuous time (real-time) without recording paused in-between?

    For example, if you are standing before a clock, you can pause the camera and the clock, take a break for 5 minutes and then get back to your last pose, resume the recording and clock simultaneously and it would be hard to tell if you had taken a pause in between. So this idea cannot be used to prove the clip is recorded continuously.

    Do you have a logical solution for this?
  2. jcsd
  3. Dec 21, 2011 #2


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    Given the fact that we can digitally edit video fairly easily these days, I would say there is no 100% foolproof way.
  4. Dec 21, 2011 #3


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    I think this is a fair question from a philosophical point of view. From a practical standpoint they have ways of discovering if something had been edited though I don't know how effective they are. I think if you have the sky behind y your back in the shot it would be tough to fake the movement of clouds and the sun
  5. Dec 21, 2011 #4
    How about buying a magazine from yesterday, showing it to the camera before E2 starts, then cite some heads on the cover, clearly enough for lip readers to confirm the text, and then put it in your pocket, somewhere where it remains visible during E2

    Probably not 100% but it's a start.
  6. Dec 21, 2011 #5


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    There is no solution, for videos in digital format. You can show that something is unlikely to be in one take by looking for inconsistencies in the images, but you can't "prove" the opposite. Anything that can be faked badly can be faked less badly, given enough effort. There's a whole industry (CGI film technology and video games) looking for better ways to fake it!

    The easiest low tech way to attempt to "prove" it would probably be to have something like smoke rising from cigarette in the image for the whole take, simply because that would be difficult (but not impossible) to fake convincingly, especially if the rest of the video content "interacted" with the smoke to show that it wasn't just a double-exposure.

    For old-style analog video recorders, you might be able to show that the tape had never been stopped and restarted by looking for any distortion or damage (stretching or scratches) caused by the mechanical stresses on the tape as it went through the recorder.
  7. Dec 21, 2011 #6


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    Nope, doesn't work. You can transfer an edited tape over to a new tape that won't show any such evidence.
  8. Dec 21, 2011 #7


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    True, but you might still get some timing glitches in the recorded signal across the edits, with analog copying. (I'm not trying to prove I'm right, just thinking of possibilities)
  9. Dec 21, 2011 #8


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    Are you trying to spoof someone for fun, or just prove for the sake of doing it you can pull the wool over others, or third, is this purely a thought problem and you don't really want to do it, or finally, want to prove others have played time games with a video clip ?

  10. Dec 21, 2011 #9
    Thanks for your replies. I am just using the Video Recording concept as an example instead of thinking in an abstract way about observation of an event with reference to time. So, don't worry about fake edits to the video and assume that the video is not edited after it's saved by the camera as an axiom. So if there are any tricks you can play, it will be only at the time of recording.
  11. Dec 21, 2011 #10
    Yes, it's a contrived thought experiment!
  12. Dec 21, 2011 #11


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    true ... I was only responding to comment about mechanical changes
  13. Dec 21, 2011 #12


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    I imagine every day where there is a once-in-a-lifetime event you could do it. For example, do it outside, during a lunar eclipse, with long exposure so you can see the constellations behind you. Most likely that angle of stars with respect to the eclipse could be calculated to an accurate date that only occurs once in a lifetime.

    Its actually a good question as it completely relies on the trust of your audience in the honesty of the image : for example:
    If I stand in front of Big Ben and it says a certain time, most people would believe the picture was taken at that time of the day. (Say noon)
    If I do the same in front of the clock at a local university, the surrounding population will believe it as its probably always right, but someone on the other side of the world may think you have the power to control what the clock says, and thus are being deceitful.
    If you take the same picture holding up your watch, very few people will believe you that it was taken at the time shown.

    Its all a matter of trust. Therefor I would say that only events captured that have happened once in your lifetime, and are scientifically verifiable, and are unable to be physically recreated without altering the video, would pass this test.
  14. Dec 21, 2011 #13
    When I was thinking on the TV idea, my brother came up with even more a challenging question: In a Universe where Retrocausality is possible but not always required(for an event to happen), would it still be possible to prove by logical reasoning the posteriority of an event?

    BTW, did you of a solution for my question on logically proving the continuity of an event?
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