A study conducted at Åbo Akademi University examined how well people are able to accurately identify people from long distances in real-world scenarios.
The study found that correctly identifying an individual from a distance of 40 metres becomes twice as difficult as accurately identifying someone who's standing five meters away. The task is complete guesswork at around 100 metres, according to the researchers.
Participants in the study were asked to identify four people, one at a time, at distances ranging between five and 110 metres. After physically seeing the person, participants were asked to identify the same individual from a series of photos of people.
Unlike in previous research on the topic, the Finnish study prompted test subjects to identify living people in physical environments, instead of only using photographs or videos.
The researchers said that identification rates could be even worse in real-life situations.
"Our findings are extremely important. We are the first to have demonstrated that there is a certain distance at which the reliability of a witness's eyesight falls to a guess," researcher Thomas Nyman said.
The data for the study was collected at the Heureka science centre in Vantaa. A total of 1,588 people aged 6–77 took part.
In a press release about the research issued by the institution last year, Nyman said: "The results from our experiment at Heureka in 2017 showed that an increase in distance had a drastic negative impact on correct identifications."