What is the exact meaning of argument?

[xuantengh]

I have no idea that what should I put into the arguments first.png and second.png. Should they be consecutive frames from one video?
Thank you very much~! ^ ^

[sniklaus]

Yes, you could take two consecutive frames from a video. That would probably be the most common scenario but you can use any pair of images for which you would like to estimate the optical flow.