Close-up photographs appear less trustworthy than photos taken from a distance, says a new study from Caltech.

The photographs taken from a distance remained pleasing to the eye even when the researchers controlled other factors that would have accounted for the change in perception like size, lighting and resolution. Study participants were shown 36 photographs of 18 different people; with one image of each individual taken from a close range and another taken from afar, approximately seven feet. 

Researchers found that geometric warping in the close-up photographs seemed untrustworthy, less attractive and less competent to the people participating in the study.

"It turns out that faces photographed quite close-up are geometrically warped, compared to photos taken at a larger distance," explained Ronnie Bryan, study author from California Institute of Technology. Nobody in the study group actually noticed the geometrical warping "nonetheless, it's a perceptual clue that influenced their judgments," added Bryan.

"This was a surprising, and surprisingly reliable, effect. We went through a bunch of experiments, some testing people in the lab, and some even over the Internet; we asked participants to rate trustworthiness of faces, and in some experiments we asked them to invest real money in unfamiliar people whose faces they saw as a direct measure of how much they trusted them," said Ralph Adolphs from California Institute of Technology.

Researchers found that almost everyone judged a photograph taken from a distance of two feet as less trustworthy than the one taken from say seven feet. They chose to include these two distances in the study because one falls within personal space and the other outside of it. Personal space is anywhere between three and four feet from the body.

In one of the experiments, researchers changed the geometric symmetry of the photograph using a computer that resulted in the photographs being perceived as less trustworthy. Researchers say that they can create a computer program that can calculate the distance between the photographer and the subject by analyzing geometric warping in the photograph.

"The work might also allow us to estimate the perceived trustworthiness of a particular face image. You could imagine that many people would be interested in such applications-particularly in the political arena," said Pietro Perona from California Institute of Technology.

Which side of a person's face is facing a photographer is also important as other studies have found out that people are more likely to find left side of the face to be more attractive than the right side.

The study is published in the journal PLoS ONE