Single buffer / frame disposal effect

have simple animation that has an object set against a transparent background. I want to render it so that the current frame is overlaid onto the previously rendered frames. See example below:

This “effect” can be seen if, in imagemagick you set frame disposal to none when converting to gif (which reduces quality) or if you use single frame buffers in some 3D rendering programs. Or, you may have seen it in Solitaire.

Does anyone know how I could do this in Blender? Currently I have to render the scene out once and then, using the Compositor, merge the current and previous frame. It would be preferable if I could it without essentially rendering twice.

Dynamic paint using a brush with image as source. But its very memory intensive and can be poor quality. Blender isnt designed to do this sort of thing.

Try this solution:

Too bad I don’t know scripting well enough, otherwise I’d try seeing if there were a way to load a previously rendered and saved sequence image as the input image. Basically have it load the previous sequence number as the image input. If image input filepath is scriptable, this really would be easy to do with alpha-over.

I do know it’s possible to do that process manually, but it’s time consuming to render out and then setup the background for who knows how many steps.