Reconstruction of drawing sequence from video I have a video that record the drawing sequence with a pencil by a painter.

I want to reconstruction the sequence from the video.
And I have google some keywords like "drawing sequence reconstruction", "sketch reconstruction", and have searched like "moving object detection" but cannot found what I want to find.

I want to know how to detect and recognize the drawing between different frames. I have thought the "line detect" algorithm may work but fail. And pixel comparison seems to be bad idea. Because that the new drawing may overlap the old ones. 

Could you give me some information that I can read or some keywords to search? Sorry about that because I am not familiar with Computer Image Processing.
You should have a look at background segmentation algorithms. The hand is moving over the rather static drawing. One very simple approach would be to store the last N images and compute the variance of the color for each pixel. The pixels with a low variance will be your painting (and the canvas you draw an) so a subsequent thresholding should seperate the drawing from the canvas.