I have taken an video of the following static scene for 10 mins (3 frames/Sec); totally 1800 frames for 10 mins.
I also show here the pixel time series, that is, a set of values of a particular pixel say (1,1) for 1800 frames..
I could see a linear trend in the series. For some pixels the trend is increasing and for some the trend is decreasing. Due to trend, though the scene is static, there appears to be a small movement in the object. It is possible to de-trend it.
My Question is: what are the causes of this trend? I use a standard camera fixed on a immovable plane and I illuminate with light in order to photograph it.