Katie Couric slimmed down in the blink of a CBS eye. Tiffany Network officials admitted yesterday that an airbrushed photo making the bubbly broadcaster appear several dress sizes smaller appeared in its promotional magazine "Watch!" The incoming "CBS Evening News" anchor said she didn't know about the digitally doctored photo until the September issue of the quarterly glossy landed on her desk. "I liked the first picture better because there's more of me to love," the 49-year-old former NBC "Today" show host said, laughing off the manipulated publicity shot.