Object detection in image sequences has a very important role in many applications, such as surveillance systems, tracking and recognition systems, and coding systems. We are interested in background subtraction, which is very popular algorithm for object detection in image sequences, and also concerned to use the result of detection in selective video coding. Especially when the camera moves and zooms in on something to track the target under drastic illumination change, it is very hard to detect the object properly, and the coding efficiency is reduced. So we generate a multiple background mosaic system, called the background mosaic plane, and use it for object detection and video coding. Some experimental results for both object detection and video coding in various environments show that the average performance of the proposed algorithm is good.