Image copyright HANNAH GAL / SPL Image caption Approachable? Intelligent? People's responses to 1,000 photographs were used to build the model 
 
 Whether it's a curled lip or a keen cheekbone, we all make quick social judgements based on strangers' faces. 
 
 Now scientists have modelled the specific physical attributes that underpin our first impressions. 
 
 Small changes in the dimensions of a face can make it appear more trustworthy, dominant or attractive. 
 
 The results, published in the journal PNAS, could help film animators or anyone looking to create an instant impression on a social network. 
 
 Dr Tom Hartley, a neuroscientist at the University of York and the study's senior author, said the work added mathematical detail to a well-known phenomenon. 
 
 "If people are forming these first impressions, just based on looking at somebody's face, what is it about the image of the face that's giving that impression - can we measure it exactly?" 
 
 Three key dimensions of a first impression Approachability: how likely is this person to help (or hinder) me? 
 
 Dominance: how capable is this person of carrying out those intentions? 
 
 Attractiveness: is this person young and good looking - a potential romantic partner? 
 
 Positive first impressions are especially important in a world dominated by social media, from LinkedIn to Tinder. 
 
 Dr Hartley sees the commercial potential in applying his numerical model to the photos people use to present themselves online. "It's obviously potentially very useful," he told the BBC. 
 
 To make the calculations, each of 1,000 face photos from the internet was shown to at least six different people, who gave it a score for 16 different social traits, like trustworthiness or intelligence. 
 
 Overall, these scores boil down to three main characteristics: whether a face is (a) approachable, (b) dominant, and (c) attractive. 
 
 Media playback is unsupported on your device Media caption Cartoon faces based on the new mathematical model, sliding along 3 scales: approachability, dominance and attractiveness 
 
 By measuring the physical attributes of all 1,000 faces and putting them together with those scores, Dr Hartley and his team built a mathematical model of how the dimensions of a face produce those three impressions. 
 
 The next step was to get the computer to extrapolate. Using their new model, the team produced cartoon versions of the most (and least) approachable, dominant and attractive faces - as well as all the possibilities in between. 
 
 Image copyright T Hartley / PNAS Image caption Six faces and their computerised approximations, including study author Dr Tom Hartley (second from left) 
 
 Image caption The same treatment given to the Today programme's John Humphrys 
 
 You could use these kind of numbers to decide when is a good time to take a photograph, or to choose the photograph that's really optimal in putting forward the best possible impression Dr Tom Hartley, University of York 
 
 Finally, and most importantly, these cartoon results could be tested. When the researchers quizzed more participants about their impressions of the artificial, cartoon faces, the ratings matched. People said that the computer's cartoon prediction of an approachable face was, indeed, approachable - and so on. 
 
 So has all this work revealed humanity's ultimate trustworthy jawline, or the most assertive shape for eyebrows? Dr Hartley is cautious. 
 
 "Lots of the features of the face tend to vary together," he explained. "So it's very difficult for us to pin down with certainty that a given feature of the face is contributing to a certain social impression." 
 
 There are some obvious trends however - including the tendency for masculine faces to be perceived as dominant, or for a broadly smiling face to seem more approachable and trustworthy. 
 
 This points to a potentially worrying implication: brief facial expressions can make a big difference to how we are received by strangers. 
 
 "It might be problematic if we're forming these kind of judgements based on these rather fleeting impressions," Dr Hartley said, "particularly in today's world where we only might see one picture of a face, on social media, and have to form our impression based on that." 
 
 Image copyright T Hartley / PNAS Image caption A mathematical model produced cartoon faces based on how people rated various facial dimensions 
 
 On the other hand, the findings could help people put their best face forward. 
 
 "It might be very useful for organisations who are interested in people's faces," said Dr Hartley. 
 
 [Being] approachable is tied to smiling expressions and unapproachable to frowning or angry expressions, while dominance is tied to masculine features Dr Anthony Little, University of Stirling 
 
 That might include interests as diverse as photographers, Facebook and Pixar. 
 
 "You would be able to use these kind of numbers to decide when is a good time to take a photograph, or maybe to choose the photograph that's really optimal in putting forward the best possible impression - and you might want to put forward different kinds of social impressions in different situations." 
 
 Animators, on the other hand, "have to give life, and give some social meaning, to the faces of their characters just by changing small things," Dr Hartley said. 
 
 "What we're doing is trying to put that on a scientific footing. It's been fascinating to find out more about it." 
 
 Dr Anthony Little, a reader in psychology at the University of Stirling, said the findings point to something "simple and important" about the way physical attributes guide our social responses. 
 
 Image copyright Thinkstock Image caption Impressions included attractiveness and trustworthiness - potential mate or used car salesman? 
 
 "The results highlight that the way we see other people may be in relatively simple terms, as approachable/unapproachable and dominant/submissive," said Dr Little, whose own research on faces and psychology includes using a website to crowd-source ratings. 
 
 "Each of these two factors looks to be tied to specific face features. So, approachable is tied to smiling expressions and unapproachable to frowning or angry expressions, while dominance is tied to masculine features. 
 
 "The third factor, youthful-attractiveness, appears less distinct." 
 
 This is because of interplay between attractiveness and the other two factors, Dr Little explained. ||||| A computer model has found a smiling expression is key to a first impression of being approachable, while large eyes signal youthfulness, and dominance is linked partly to a masculine face shape. 
 
 You may think you can judge a person you just met based on his or her facial expressions. Does a smile indicate a person is easygoing or insincere? Does squinting show concentration, or mistrust? 
 
 First impressions of people — such as whether they are trustworthy, dominant or attractive — can develop from a glimpse as brief as 100 milliseconds or less. Brain scans suggests that such judgments are made automatically, probably outside of people's conscious control. 
 
 But now, a computer system that mimics the human brain has identified which facial features most influence how others first perceive a person, scientists say.These findings could lead to computer programs that automatically see which photographs would help people give the best first impressions they can, the researchers added. 
 
 Because first impressions can affect people's future behavior and can be difficult to overturn, "it's useful to know how we're being judged on our appearance, especially since these judgments might not be accurate — think of effects on court cases or democratic elections, for example," said study co-author Tom Hartley, a cognitive neuroscientist and psychologist at the University of York in England. "Should we really trust a smiling face?" [Smile Secrets: 5 Things Your Grin Reveals About You] 
 
 Although some previous research has suggested that there may be a kernel of truth in some first impressions, Hartley noted that people typically go too far with the judgments they develop from first impressions. "For instance, someone with a young-looking face is judged to have other immature characteristics," Hartley said. "Evidence is clear that often judging a book by its cover is just plain wrong, but we all do it." 
 
 Given the increasing presence of faces on social media sites, first impressions could be more important than ever, Hartley suggested. 
 
 "Whereas, in the past, we got to know people through meeting them in the flesh, increasingly, our first contact is online, and our first impressions are based on the images we provide on social media profiles," Hartley told Live Science. 
 
 Previous research has shown that "the many different judgments characterizing first impressions tend to fall along three underlying dimensions," Hartley said. "One is approachability — do they want to help me or to harm me? The next is dominance — can they help or harm me? The last is youthful-attractiveness — perhaps representing whether they would be a good romantic partner or rival." 
 
 Judging images 
 
 To learn more about how first impressions are formed, the research team at the University of York found 1,000 photographs of people on the Internet, and showed them to six volunteers. The participants rated their first impressions of the people in the photos on social traits such as trustworthiness and dominance. These images were typical of pictures seen every day, ranging widely in angle, lighting, ages, expressions, hairstyles and so on. 
 
 Each face was broken down into 65 physical features, such as the shape of a person's jaw, mouth, eyes, cheekbones or eyebrows. The researchers then analyzed these faces using an artificial neural network, a kind of artificial intelligence computing system that mimics how the brain works. They had the neural network attempt to learn which facial physical features might be linked to first impressions of social traits. 
 
 This modelsuggested "that given enough data, we can accurately gauge people's likely impressions of a given image," Hartley said. "If you're thinking about attaching a picture to their CV, résumé or online dating profile, maybe you should take a look at our paper first!" 
 
 The model found that mouth shape and area were linked to approachability — unsurprisingly, a smiling expression is a key component of an impression of approachability. When it came to youthful-attractiveness, eye shape and area were important, in line with views linking relatively large eyes to a youthful appearance. Dominance was linked with features indicating a masculine face shape, such as eyebrow height, cheekbones, as well as color and texture differences that may relate to either masculinity or a healthy or tanned overall appearance. 
 
 "Our results suggest that some of the features that are associated with first impressions are linked to changeable properties of the face or setting that are specific to a given image," Hartley said. "So, things like expression, pose, camera position, lighting can all, in principle, contribute alongside the structure of our faces themselves. In some ways, our model parallels or makes explicit the kinds of judgment that might be relevant to casting directors, animators and portrait photographers who select or manipulate images to create certain impressions." 
 
 Wanna look more trustworthy? 
 
 By reversing this process, the researchers created a model that generated cartoon faces depicting the typical characteristics of someone judged as having certain social traits. The researchers compared the results with those of 30 human judges, and found that these cartoon faces usually gave the first impressions they were designed to give. [7 Personality Traits You May Want to Change] 
 
 Hartley suggested that future research might be able to use these findings "to select an image which conveys a desirable impression, perhaps even automatically." 
 
 However, Hartley noted that the researchers looked only at Caucasian faces in this study, to avoid possible confounding effects of race, though they are currently conducting cross-cultural studies to find out how culture impacts the results. 
 
 "We know that people process faces of other ethnicities differently from their own — this might be because of cultural stereotypes, but also more subtle things such as the level of experience we have with different kinds of variation in the face," Hartley said. "As it's not practical to incorporate faces and judges from every possible geographic, cultural and ethnic background, we instead try to keep these factors fixed by focusing on one ethnic and cultural group at a time. We can then investigate the ways in which different groups rely on different facial features and perhaps reach different social judgments in a step-by-step way." 
 
 In addition to looking across cultures, future studies can also "use brain imaging to investigate how these social impressions are created in the brain," Hartley said. Another direction for research "will be to look at ways in which first impressions can be influenced by directly manipulating specific features, and whether, with the knowledge we now have, we can influence people's social decisions by choosing images with particular characteristics," he added. 
 
 The scientists detailed their findings online July 28 in the journal Proceedings of the National Academy of Sciences. 
 
 Follow Live Science @livescience, Facebook & Google+. Original article on Live Science. ||||| Within moments of meeting someone new, we've make both conscious and subconscious judgments about them—even if we're just looking at a picture of them. First impressions largely hinge on a person's facial features, which we judge on three major axes: dominance, approachability and attractiveness. Now, researchers publishing in Proceedings of the National Academy of Sciences have revealed the underpinnings of our snap judgments. 
 
 To create a model that could predict first impressions, the team first asked volunteers to record their first impression of more than 1,000 photos of people's faces, taken from the internet, the BBC reports. Then, the researchers built a model based on careful measurements of the faces combined with the respondents' first impressions. 
 
 To test how accurate their program was, the researchers used it to generate cartoon faces representing different first impressions of dominance, approachability and attractiveness, the BBC continues. They asked volunteers to make judgments about both the cartoons and the real-life faces they represented and found that the impressions matched. 
 
 The team thinks their findings could help animators create more convincing characters, as well as aid those looking to make a good first impression through an application photo or social network profile picture, the BBC adds.
– Have masculine or feminine features? A big smile? Characteristics like these, it seems, are central to our snap judgements of people's faces. Using a computer model, researchers have figured out how different features affect our first impressions, the BBC reports. The system is based on 1,000 pictures of different faces gathered online. In a study, researchers had respondents give opinions of these faces, focusing on approachability, dominance, and attractiveness. Researchers then created a mathematical model that translated those opinions into distinct facial measurements—an effort to "crack the code of first impressions," notes Smithsonian. The result was a computer program that generates cartoon faces intended to be dominant or submissive, approachable or off-putting. Another batch of study subjects offered their opinions of the cartoons—and they fit the computer's assessments. Masculine features and a good tan were apparently tied to the perception of dominance, while smiles were associated with approachability, LiveScience reports. Knowing how first impressions work may be particularly important these days: "Whereas in the past, we got to know people through meeting them in the flesh, increasingly, our first contact is online, and our first impressions are based on the images we provide on social media profiles," says the study's lead author. Of course, what's attractive could change a lot in the next century.