Backlight is created by taking pictures of your pet with the strongest light behind them. It is a powerful way to frame and highlight your pet but can easily go wrong. It is important to expose for the face at the risk of causing the backlighted areas to blow out. You can prevent the picture from becoming heavily overexposed by placing your subject against a dark background. This makes exposure easier and will add prominence to the highlighted halo of fur around your pets face and body.
