How did he put the same drawing in the 2 frames?

I saw someone in a video who drew something in a blank frame and in the other blank frame there was also the same drawing, how did he do that?
is that, when I make a drawing in a frame, in the other frame there is nothing, but in a video it was seen that it had the same drawing in the other frame, and it was not seen that it had copied it or something, there is a key to that or how?