How to save full-sized images with overlays from a figure window?

I have a matlab figure that contains an image. In the figure, the image has lines and circles drawn on it. The image is relatively large (3k x 4k) and is therefore resized by Matlab's figure display method. I want to save the image and the objects plotted over it in the original resolution of the image. The plots would have to be scaled up from the size they are in figure and combined with the pixels in the image -- overwriting the pixels that they overlay. It is not one of my programs that generates the figures from my image. It plots on my image in the figure. But I want to save the image in its original size with the overlays merged into it. To further complicate matters, I have a sequence of images being so displayed as a sequence of figures. So I want to write a script that accesses each figure and saves the image it displays at the image's full original resolution (as say a png file) with the plotted graphics in the figure rescaled to match the original resolution of the image.

How can I do that?