WHEN John Knoll created Photoshop in 1989, he knew he was designing an image-editing program that could be used in good ways and bad. But even Mr. Knoll, who wrote the software with his brother, Tom, was unprepared for how outlandish photo manipulation would become. "When we worked on it, mostly we saw the possibilities, the cool things," said Mr. Knoll, 41. "Not how it would be abused." The same tools that can be used to crop, retouch and otherwise edit digital images can be used just as easily to distort, alter and fabricate them. With Photoshop and similar programs...