You can in most cases connect your camera to your computer and use 'browse' to view your photos and select one. Another option is to copy your photo to the My Pictures folder, or any other folder, on your computer. Most laptop computers also have a flash card slot for your camera's memory card, allowing you to browse the photos on that card and upload one.
Flashing is likely to create shadow in the background, which will probably lead to rejection of your passport photo. Another reason is that flashing often leads to red eyes, which is also unacceptable. In any case, photos without flash provide for a much more natural looking facial image.