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NOVA scienceNOW: Profile: Hany Farid
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Viewing Ideas
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Before Watching
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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.
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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).
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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.
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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 supply stores.
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Randomly distribute an image and one grid to each student.
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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.
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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 images?
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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)
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Revisit the gridded images and this discussion after viewing
the video.
After Watching
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Spot 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?
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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 activity.
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 time available.
For most manipulations, students will probably use the following
tools, found on most image processing software programs:
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Lasso, which allows one to select part of an image by
drawing around it;
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Magnetic 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;
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Magic Wand, which selects part of an image by color; and
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Quick 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.
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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
shadows.
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
various setups.
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.
Extension: 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 or scene.
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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.
Start 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?
Web Sites
NOVA scienceNOW
www.pbs.org/nova/sciencenow/0301/03.html
Presents an activity that offers the opportunity to differentiate
between doctored and untouched photos, and includes
Ask the Expert.
PBS: History Detectives
www.pbs.org/opb/historydetectives/investigations/210_forgeries.html
Provides general information on how to detect forgeries.
New York Times: Proving That Seeing Shouldn't Always Be Believing
www.nytimes.com/2007/10/02/science/02conv.html
Offers an interview with Nay Farid.
Hany Farid's Web Site: Photo Tampering Throughout History
www.cs.dartmouth.edu/farid/research/digitaltampering
Presents a series of example image forgeries with brief
explanations of what was done to create each.
Adobe Photoshop online support
livedocs.adobe.com/en_US/Photoshop/10.0/index.html
Offers general instructions on use of the image-processing
software.
Books
Crime Scene: How Investigators Use Science to Track Down the Bad
Guys
by Vivien Bowers and Martha Newbigging.
Maple Tree
Press, February 2006.
Introduces forensic science, including
means of detecting counterfeit money and forged documents
Digital Photo Madness!: 50 Weird & Wacky Things to Do with
Your Digital Camera
by Thom Gaines.
Lark Books, May 2006.
Provides tips
on using a digital camera, basic photography skills, and project
ideas.
Digital Camera Tricks and Special Effects 101
by
Michelle Perkins.
Amherst Media, January 2006.
Describes
how to make unusual effects with a digital camera and common
image-manipulation programs.
How to Understand, Enjoy, and Draw Optical Illusions: 37
Illustrated Projects
by Robert Ausbourne.
Pomegranate Communications,
September 2007.
Explains how optical illusions work and how
they can be created.
Masters of Deception: Escher, Dali & the Artists of Optical
Illusion
by Al Seckel.
Sterling, August 2007.
Offers
beautiful and compelling optical illusions that play with our
perceptions
Adobe Photoshop CS3 Classroom in a Book
by Adobe
Creative Team.
Adobe Press, April 2007.
Offers clear,
step-by-step lessons on the basic and advanced features of the
software.
Activity Author
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.
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