Book excerpt: In Camera Clues , Joe Nickell shares his methods of identifying and dating old photos and demonstrates how to distinguish originals from copies and fakes. Particularly intriguing are his discussions of camera tricks, darkroom manipulations, retouching techniques, and uses of computer technology to deceive the eye. Camera Clues concludes with a look at allegedly "paranormal" photography, from nineteenth-century "spirit photographs" to UFO snapshots.