In this paper, an extensive survey on PLD methods for low-altitude aircraft safety based on image processing is presented. First, primary features of power lines are introduced. Then, main studies on PLD are summarized, including PLD approaches based on tradition image processing methods and machine learning. Besides, a few latest research works, such as PLD based on deep learning and infrared images, are discussed. By discussing and comparing current methods, we have proposed future development directions of PLD, with the aim of providing a starting point for researchers in PLD. Specifically, image fusion and multimodal sensor fusion should be able to provide better detection performance and lower false alarm rate by exploiting complementary information from different sensors. In addition, AI will be an important technique in PLD, with the help of transfer learning to utilize limited training data and of multimodal learning to deal with different kinds of information.