Back to Teachers Home

NOVA scienceNOW: Profile: Hany Farid

Viewing Ideas

Before Watching

1. 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.

2. 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).

3. 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.

   1. 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.

   2. Randomly distribute an image and one grid to each student.

   3. 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.

   4. 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?

   5. 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)

   6. Revisit the gridded images and this discussion after viewing the video.

After Watching

1. 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?

2. 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:

   • Lasso, which allows one to select part of an image by drawing around it;

   • 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;

   • Magic Wand, which selects part of an image by color; and

   • 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.

3. 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.

4. 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.