Photobooth doesn't have a flash, but it simulates one by flashing the screen of your computer white when it takes a picture. This generates some amount of light to help give you better pictures. But there may be times when you don't want the flash. If you want to take a picture in PhotoBooth without the "flash" going off, hold down the Shift key when you click to take the picture and PhotoBooth will take the picture without flashing the screen.