1. An object detection system, the system comprising: a far IR sensor operable to sense thermal radiation of objects and surroundings in a field of view and to generate a far IR image in response thereto; and an image processing device operable to receive and process the far IR image to detect the presence of one or more objects in the field of view, the image processing device is configured to process the far IR image by generating an initial threshold image based on the far IR image and an initial threshold value, iteratively obtaining a number of successive threshold images based on the far IR image and a number of successively increased threshold values, and determining the presence of one or more objects in the field of view based on the initial threshold image, the number of successive threshold images, the initial threshold value and the successive threshold values.