This article shows you how to extract the frame (picture) of a video
Once you have installed ffmpeg, you can execute the following command.
ffmpeg -i input.mp4 -vframes 20 output_image_%03d.jpg
ffmpeg -i input.mp4 -vf "select=eq(n\,30)" -vframes 1 output_image.jpg
ffmpeg -i movie.mpg movie%d.jpg