Like photos, videos can be edited with different degrees of subtlety. Manipulated videos are harder to detect than manipulated photos, but there are several online tools that you can use to help detect these manipulations, which are becoming more and more common.

Using the InVID verification plugin (download here, use the "Forensics” tab), you can upload screengrabs of videos (either physical screengrabs or links) and try to identify where the image has been modified. The site Forensically has similar features. But be careful, such tools aren't always conclusive.

Here’s an example. This video, showing American anti-gun activist Emma Gonzales, was modified in March 2018 to make it look like she was ripping up the US Constitution. Conservative trolls took a video where she rips up a paper shooting target and replaced it with the Constitution, using a technique called “motion tracking”.

If you put this altered video through InVid, then the online tool notices that there is something fishy. Below, you can see that the Constitution is much darker than the rest of the video. That means that the quality of the image is different in these two regions and that the video was probably altered.

You get a more definitive answer if you put a photo from the video into the tool.

In the different filters, you can see that there is clearly something different about the space of the screen that shows the paper Gonzales is holding. That’s a clue that this video was probably manipulated.

Here, the two results - for the video and then the photo - are different because the qualities of the two images are different. It is harder to identify a digitally altered video because you have to take screengrabs, which alter the quality of the image and provide less detail. Lower quality images hide rough edges and can diminish signs that the footage has been altered.

To spot these altered videos, you need to pay close attention to details and develop good investigative reflexes. Importantly, you need to remember that these tools don’t always reveal the truth - they are just tools to help us with our research.

>> READ MORE ON THE OBSERVERS : Basic tricks to avoid internet hoaxes
Increasingly advanced techniques
These days, techniques used to alter videos have reached alarming levels of sophistication. The University of Washington managed to manipulate how former US President Barack Obama moved his mouth using 14 hours of footage of his speeches. They can now make videos where the president says whatever they want him to say using an imperceptible synthetic voice and realistic movements of his mouth.

You can see an example of this below, or by clicking this link.

Some celebrities have fallen victim to a technique known as “face-swapping,” which pastes a person’s face onto the body of someone else, often performers in porn videos.

On discussion forums like Reddit et 4chan, the threads talking about these manipulation techniques have thousands of members, says French magazine Les Inrocks.