NOVA scienceNOW: Profile: Hany Farid
Explore optical illusions: You can't always believe your eyes. Consider,
for example, optical illusions. Optical illusions play with the visual clues we
use to interpret what our eyes see. As the segment shows, Hany Farid also takes
advantages of visual clues—clues that tell him that what we are seeing
isn't to be believed.
Show students a series of optical illusions: Use the "See also" links at the bottom of
the page to move through the illusions and explore how each one tricks the eye.
Have students study the "Bump" illusion,
which illustrates how our eyes and brain use shadows and the positions of light
sources to interpret what we see. Ask students to describe which direction the
light is coming from if the they are seeing a depression or a raised figure. In the video, Farid describes how he uses shadows and light
sources to spot faked images. While watching the segment, have students record
the kinds of clues Hany uses to recognize faked images.
Create a faked image: Before class, collect magazines and other sources
of images that students can cut apart. Then, in class, have your class use the
magazines, scissors, and glue sticks to create faked images, such as various
celebrities standing together, someone being attacked by a giant cat, or a palm
tree growing in the desert. Students should attempt to make their composite
images as realistic as possible. To get started, consider showing the class
examples from Hany Farid's Photo Tampering
Throughout History Web page.
When your students are done
creating their fake images, have them share the images with a group or with the
entire class. Which seem most believable and why? Have students point out what,
beyond just the obvious cut lines, gives away the fact that they are fake.
After viewing the video, look at this collection of forgeries again. Now that
students know more about Farid's work, what new clues can they point out
that give away the fact that their composites are fake (e.g., shadows, light,
glint in eye, perspective).
Explore pixels and the nature digital
images. In order for students to
understand the nature of image fakery, it is important that they understand the
nature of electronic images. A digital image is made of a grid of pixels. Pixels are the smallest elements that make up an image.
They are the squares or dots one sees as one zooms-in on an image. The more
pixels there are within a given area, the sharper the image (i.e., the higher
the resolution) and the farther you can zoom in before the "dots"
become noticeable. Each pixel has one and only one value—a particular brightness
in a grey-scale model, RGB (Red-Green-Blue) model, or other color model. Fakery
can often be identified by inconsistencies in the pixels.
Gather images from magazines and newspapers.
Also get sheets of graph paper with the following grid sizes: 1-inch/2-cm
squares, half-inch/1-cm squares, and quarter-inch/half-cm squares. Grid paper
is available in supplementary math books, on the Internet, and from office
Randomly distribute an image and one grid to
Have students lay their grid over their image.
Have them assign each grid square either a black, gray, or white value,
according to the darkness of the part of the image under the grid square. For
example, if the part of the image under a grid square is mostly dark, students
should color it black; if it is partially dark and partially light, students
should color it gray; and if it is light, students should leave the grid square
white. NOTE: Using a light table or holding the image and graph paper up to a
window will facilitate the process of transferring the image onto graph paper.
Have your students compare and discuss their
completed grids. Is their image recognizable? Which grid sizes make it easy to
tell the features in an image—those with many, small squares (pixels) or
those with fewer, larger squares? (The more squares there are, the easier it
will be to determine an image's features.) For students with the same original images, how do different
grid-versions look? For students with both the same images and grids, do the
grid-versions of the image look the same? What is the grid-size threshold for
recognizing an image and how does this threshold vary for certain types of
Extend the discussion to what students should
pay attention to if they were trying to make a believable fake. (Keep the
grid size consistent; Get the grid lines to line up; Match the scale of the
subjects within the image; Keep the lighting consistent)
Revisit the gridded
images and this discussion after viewing the video.
a faked image. Hany Farid has
sophisticated tools to help him identify a faked image, but he also has a keen
eye for simply spotting possible fakes. Looking at imagery with a critical eye
is a habit and skill anyone can develop. Before class, buy a number of tabloids
and magazines (or print images from tabloid Web sites or Hany Farid's site),
looking through them for any inappropriate material before giving them to your
students. Then, in class, challenge your students to identify images that they
think are manipulated in some way—anything from airbrushing to outright
fakery. Have them explain their reasoning. What clues make them think it was
manipulated? How certain are they? What would make them more certain? What
would convince them it wasn't manipulated? Assuming it was indeed
manipulated, what was the purpose of the manipulation and what are the
consequences of the manipulation in terms of influences on the viewer?
Create a forgery. Manipulating an image is a combination of art and science. It can be
done with any image-processing program. Note, however, that there is a learning
curve on using these programs—if your students are unfamiliar with the
software or with working on digital imagery, this may not be an appropriate
Challenge your students to use
the software to create a believable fake image. For example, can they place a
person in a new location, put someone's head on someone else's
body, make a "giant" lizard attack a skyscraper, or erase a horse
from underneath its rider. Such fakery involves selecting parts of images for
copying and pasting, manipulation, or erasure. Students can become deeply
engaged in this kind of project; make sure they complete their projects in the
For most manipulations, students will
probably use the following tools, found on most image processing software
which allows one to select part of an image by drawing around it;
Lasso, which assists with drawing around and selecting part of an image, if the
edge of the feature to be selected is clear and the contrast strong;
Wand, which selects part of an image by color; and
Mask, which allows selected regions to be manipulated without affecting other
parts of the image or to be copied and pasted to another location or image.
Once the forgeries are created,
print out or otherwise display a series of before and after pictures. Have the
class discuss which of each pair is the fake, what gives the fakery away, and
how the fakes could be improved with more time or practice. Have students refer
to the fakery-clues presented in the video segment.
Experiment with Light. In the video, Hany Farid explains how
inconsistencies in light sources and shadows are one of the primary clues he
uses to detect a faked image. In order to spot inconsistencies, it is important
to first have a feel for how light and shadow work. As demonstrations in front
of the class or at stations around the room, have your students explore
Begin by turning off the overhead lights
and darkening your classroom as much as possible. Then, with a paper towel
roll, toilet paper roll, and light source, explore how objects of different
heights (e.g. buildings, trees, or people) cast shadows. Try various
setups—moving the light source to different positions, adjusting the
placement of the rolls relative to each other and the light source, or changing
the surface on which the rolls are standing. For each setup, have your students
make two drawings that include the tubes, light source-positions, and shadows.
In one drawing, students should make the shadows as correct as possible. In the
other, they should draw the shadows so they are incorrect in some way. Have
student pairs or groups compare drawings. We experience light and shadow in a
way that is always consistent. Point out how deeply ingrained our perceptions
are. Consequently, it doesn't take much change to jar our sense of how
things should be.
As you prepare and explore various
setups, consider the following questions: Do the shadows point in the same
direction? (Depends on the light source or sources) Can you make them point in the same direction? (Yes,
by shining the light onto both tubes from the same side) Can you make them point in very different
directions? (Yes, by putting the light source between the standing
tubes or by putting them on a surface with dips and ridges) How do the lengths of the shadows compare? (Depends
on various factors, especially the angle at which the light is shining.
Generally, the taller tube will have the longer shadow) Can you make them be very different in length? (Yes.
Tubes set at different distances from a light shining from the side will be
different length.) Can you make them be the
same length? (Yes, the shadows can be the same length if the light is
shining close to straight down on the tubes.)
Extension: Extend the explorations by adding in an additional
light source. Can you get shadows being cast in different directions? Can you
tell which light source is closer to a roll by the nature of the shadows cast?
Can you get the shadows to (largely) go away? As before, prepare and draw
Extension: In the video, the graduate student Kimo Johnson
introduces the idea that the reflections in people's eyes can provide
information on the lighting, and Hany expands on this, showing how the
reflections in his eyes indicate the direction of the light source; he's
even used this information to create software that can analyze eye reflections.
Using marbles and a light source, explore how light reflects off a sphere such
as the eye. How does the direction of a light source relate to the placement of
reflections on the marbles? What affect, if any, does distance have? As before,
prepare and draw various setups.
Do the activity using Halloween
masks, pose-able action figures, dolls, busts, or other model of a head or
body. Students can then actually see how light and shadow falls on a face or
torso. Point out that some movies made with computer graphics are more
realistic-looking than others. Discuss the limitations of this technology, how
well it can simulate "real" people, and the kinds of things
computer graphics artists need to take into account to make a believable person
Discuss which image manipulations are acceptable. The video segment states that Hany Farid
"spends much of his time making fakes and forgeries—images that are
meant to trick the human eye." However, it then goes on to explain that
"Hany is not a forger or a crook." What Hany does is important to
the science of digital forensics; it is a means to a worthwhile end. But when
is image manipulation acceptable and when is it unacceptable? Lead your class
in a discussion of, or have teams of students discuss, various types of image
fakery and when they think it is acceptable, borderline, or unacceptable.
by listing various types of image manipulation (e.g., tabloid composites,
advertising tricks, airbrushing of models, political propaganda, special
effects and "movie magic," etc.)
And as seems appropriate, show examples of various image manipulations on Hany
Farid's Web Site: Photo Tampering Throughout
History. Ask students' opinions of which types of
manipulation are never acceptable, sometimes acceptable, or always acceptable.
In what settings or under what circumstances are image manipulations
acceptable? Are there purposes (e.g. entertainment, political, business or
sales) that make image manipulations acceptable or completely unacceptable? When
is image manipulation so deceptive as to be malicious? How does the intention
of the faker play into the issue?
Presents an activity that offers the opportunity to differentiate between doctored and untouched photos, and includes Ask the Expert.
general information on how to detect forgeries.
Times: Proving That Seeing Shouldn't Always Be
interview with Nay Farid.
Farid's Web Site: Photo Tampering Throughout
series of example image forgeries with brief explanations of what was done to
Photoshop online support
general instructions on use of the image-processing software.
Scene: How Investigators Use Science to Track Down the Bad Guys
Vivien Bowers and Martha Newbigging.
Maple Tree Press, February 2006.
forensic science, including means of detecting counterfeit money and forged
Photo Madness!: 50 Weird & Wacky Things to Do with Your Digital Camera
Lark Books, May 2006.
tips on using a digital camera, basic photography skills, and project ideas.
Camera Tricks and Special Effects 101
Amherst Media, January 2006.
how to make unusual effects with a digital camera and common image-manipulation
to Understand, Enjoy, and Draw Optical Illusions: 37 Illustrated Projects
Pomegranate Communications, September 2007.
how optical illusions work and how they can be created.
of Deception: Escher, Dali & the Artists of Optical Illusion
Sterling, August 2007.
beautiful and compelling optical illusions
that play with our perceptions
Photoshop CS3 Classroom in a Book
Adobe Creative Team.
Adobe Press, April 2007.
Offers clear, step-by-step lessons on the basic and advanced
features of the software.
Teon Edwards is a curriculum
developer with a background in astrophysics, mathematics, and the use of
technology and multimedia in teaching and learning. Since 1996, she has
developed numerous science and mathematics education materials for school,
home, and informal learning environments.