We have evolved to be amazingly good at seeing faces. From the point of view of evolution, success would certainly have favored those who were good at spotting the faces of a predator in the brush, for example. We see faces everywhere. We are so good at spotting faces that we even see them where they do not exist. In fact, said Carl Sagan, "As an inadvertent side effect, the pattern-recognition machinery in our brains is so efficient in extracting a face from a clutter of other detail that we sometimes see faces where there are none." This would explain why people see an image of Mother Teresa in a cheese sandwich or a face on Mars. (More fantastic examples of "faces.") Faces—and things approximating images of faces — get our attention. Graphic designers and marketers know this very well, which is why you so often see faces in various forms of marketing communication.

 
Above: We are wired to see faces. Even babies take note of faces and eye gaze and pay special notice to those faces that are familiar. During my live TEDxTokyo talk streamed back home in our kitchen my daughter notices a relatively small, low resolution 2-D video of her father. At only 13-months she knew who that was on screen and was glued to the imagery, often pointing and shouting "dada!"


Above: In a sea of clutter, a face can stick out. Notice how the image of Bob Marley gets your attention even though it is relatively tiny. In this case it is the only face; in a sea of faces it may receive less attention.

Eye gaze
When I was a small boy, my mischievous friends and I would sometimes stand in front of our house and look up high in the sky as if we saw something interesting just to see how many passer-bys would also look up in the sky. Most people who saw us did of course look up trying to figure out what we were looking at. We are naturally drawn to look in the directions which other people are looking. I noticed that even my baby daughter looks in the direction I am looking; this tendency started at an early age.

Using images of faces — even non-human faces — can be effective for getting a viewer's attention. This is especially true for mediums such as posters, magazines, and billboards, but can be applied to multimedia and large screen displays as well. Because images of faces are so effective at getting the eye's attention, they must be used with discretion. One important consideration is the issue of eye gaze and leading the eye of the viewer. For example, the two images below are from a study by James Breeze which used eye tracking software to determine if the direction the baby looked on screen influenced the eye gaze of the website readers. Not surprisingly the text on the right got more attention from the eyes when the baby's eye gaze was in that direction.

 
Above: One small eye tracking study shows the influence of eye gaze in guiding the viewer's eye on the page. (Click for larger size. Source.)

Should you use images of faces in presentations? That's up to you. My point is not to say that you should use images of people (or animals, etc) in your visuals; each context and topic is different. My point is only to say that if you do, be mindful of the power that images of faces have for getting attention and try to use eye gaze to help guide the viewer's eye. Below are some examples. I'll first look at samples from posters and billboards near my home in Nara, Japan, then I'll show some samples slides.

Samples from the world around us
I have said it a millions times, but if you take note of the graphic design around you, you'll find there are many lessons. Here are just a few below.

Above: Speeding down the freeway in Osaka. The billboard gets your attention and must be understood in a flash. Face looks in direction of the text and product (and the road ahead).

 

Above: The women in these posters are placed on the outer third and look or orientate themselves in the general direction of the ad copy or smaller product image.

 
Above: Left: The image of the celebrity is huge and gets your attention. Her gaze is not in the direction of the product or the ad copy, but to counter this everything except the beer is in black & white which makes the beer glass pop out at you. You notice the face first, but the bright color of the beer draws your eye. Right: Faces get your attention, but your eye is quickly drawn to the text and colorful beer cans.

Sample slides
I use images of people sparingly, but I often use the image of the individual who I am quoting in a slide. This makes the message more real somewhow and can add a bit of context. Also, many audience members know the face but not the name of the person quoted.

 
Above: Both famous men in these slides are looking in the general direction of the quote. You notice the face first, but your eye natually moves to the text.

 
Above: Here I am quoting Isabel Allende (see her TED talk). The slide on the right makes better use of eye gaze. The image is more natural as well since it is not cut but naturally bleeds off the right side.

 
Above: The slide on the left is acceptable, but notice how much more natural the slide on the right feels when the face of O-Sensei is orientated inward toward the bulk of the slide and in the general direction of the text.

 
Above: This is an image of Judit Kawaguchi (who writes for the Japan Times, among other things) interviewing The Dalai Lama on the Shinkansen in Japan. The quote which appears in the slide is something he said during that actual interview on the train. The first slide shows the context, then the second slide fades in which results in Judit Kawaguchi fading out and being replaced by the text; the right third of the slide (The Dalai Lama) never appears to change.

Not only human faces
We notice faces of all kinds. Even the orientation of animals in a frame can help guide the viewer's eye. Here are a couple more examples of quotes in slides, this time with birds.


Above: The context in this case was the oil spill last year in a presentation on general environmental issues.



 
Above: The broader theme the speaker was touching on related to personal freedom and fulfillment, so the image of a bird soaring high — an image I took myself while visiting the Oregon Coast — seemed fitting. The bird gets your attention and its orientation, shape, and impression of movement upward (not actual animation of course) lead your eye toward the text. The image of the bird almost acts as a big arrow saying "look here."

Related Links
• Faces, Faces Everywhere, New York Times
• Pictures of faces that are not really faces
• You look where they look
• TED Talk: Michael Shermer on strange beliefs (including why we see faces everywhere).
• I have a section on Eye Gaze and faces in the 3rd edition of Presentation Zen.