This article was taken from the June issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online
Spot a doctored photo from repeated crowd scenes at Berlusconi's political addresses to erased limbs on DVD artwork, dodgy Photoshop jobs are rife. But they are not always as obvious as the syrupy gloss of David Cameron's campaign poster face -- so what else gives the game away?
1. Check the shadows
Choose a part of an object, such as the peak of a hat. Draw a line to its corresponding shadow. It should point in the direction of the light source. Do this for more than one object, and you should get a convergence point (indoor lighting) or parallel lines (outdoor shots). If lines cross, then something's not right.
2. Look into the eyes
Hany Farid, professor at Dartmouth College, New Hampshire, and specialist in forensic imaging, says: "The eye reflects information about where a person was. In particular, the little white dots in the eyes. If there's more than one person in an image, zoom in on the eyes -- if there are white dots in their eyes they should all have the same. When people are shot in different conditions, their eyes reflect the lighting they were in -- if it doesn't match up, then it's wrong."
3. Recurring patterns
Scott Kelby, president of the NAPP (National Association of Photoshop Professionals), says: "People use the clone tool to remove things, but it can pick a detail up and repeat it, which can make a recurring pattern. You can work out where something was, and what area was cloned. It's a dead giveaway."
4. Don't confuse compression with tampering
"In very heavily compressed images you get vertical and horizontal lines," says Farid. "In addition, JPEG compresses the colour channels so it's very easy to look at an image and conclude it's been manipulated because you see weird colours and lines. If you're trying to work out if an image has been tampered with, realise what you should look for and you shouldn't look for."
5. Poor masking
Masks are used to blend images. "Bad masks expose mismatches between the edges of elements," says photographer Morgan Silk. "Look for 'fringes' and 'halos'. Edges can also look too sharp or too soft." However, sharp borders, such as black objects on white, can look like bad masks.
6. Interrogate the image with an Exif reader
To find out if an image was processed, or where it came from, interrogate it with an Exif reader (try bit.ly/ZjfA8 -- it's Windows only, though). This software scrapes the image for metadata -- information created at the time it was taken. Processing often wipes metadata, so if it's absent, it's quite likely that the image has been altered in some way.
This article was originally published by WIRED UK
