Keep residual image of an element in a video I have a video of a static background with a spider which is the only moving element.

The spider is going forward for a few seconds, then the video stops.
I want to summarize the video into a single image where the background doesn't change, but where we see each frame of the spider going forward, like a superposition. Something that I can illustrate with the following image:

I understand that I will probably need to downsample my video to a few frames, but I don't know how to do the rest. If needed I can put a green background like: (but I'd prefer not to)

EDIT: This is the kind of results that I am looking for
You'll need to separate the spider from the background somehow. Then you can stack successive images of the spider on top of the initial background, and the previous spider image frames.
here's an ascii art representation
        sp5-------------&gt;
      sp4---------------&gt;
    sp3-----------------&gt;
  sp2-------------------&gt;
sp1---------------------&gt;
bg----------------------&gt;

So on the first frame we see the BG with the first Spider frame composited above it. This frame is held, then on the next frame we add spider frame 2 and hold, then on the next spider frame 3 is added, and so on.
How you actually achieve this depends on the software you're using.