Documenting memories is no longer as difficult as it used to be. We stage, document, share and censor with taps and clicks.

But what can trigger the return of memories we could not document? What makes them rise to the surface from the recesses of our minds?

And when it comes to these “memories”, what if something didn’t actually happen the way we remember it? What it is didn’t happen at all?

These are the questions a new video (above) tries to answer.

In a study conducted in the early 2000s, subjects were treated to three real pictures from their childhood, along with one fake picture of a family outing. The picture in question was photoshopped to show a hot air balloon ride that had never really occurred.

Subjects looked at the pictures three times for two weeks, and a staggering 50% actually “remembered” the balloon ride, even offering descriptive details. It is believed that childhood memories may be the most susceptible to such manipulation.

Likewise, a study in 2011 led people to “remember” fake news from headlines accompanied by manipulated images.

How do you tell such fake memories apart from real ones, then? The bad news is you can’t, unless someone tells you. But it may be nearly impossible to verify the authenticity of images as more time goes by, and this may turn into a very real challenge in the future. One of the most unsettling things about memory and pictures then is that something can be an alt fact, but we believe it anyway.

The good news, however, is that pictures (along with music and stories) can help people with dementia recall events through reminiscence therapy. They can also improve mood and cognition, according to research.