Set image aspect ratio using imshow

I am trying to load an image (screenshot of a graph), and plot my data on top. I have achieved this, but the aspect ratio of the displayed image/graph doesn't look to be adjustable. Can it be done?

% Load cleaned up screen shot.
load image.mat

% Observe aspect ratio.
imshow(I)

% Flip matrix so that y axis origin is at the bottom instead of the top.
I = flipud(I);

% Scale image to allow plotting on top - this works, but changes the aspect ratio.
RI = imref2d(size(I));
RI.XWorldLimits = [1970 2020];
RI.YWorldLimits = [320 410];
figure;
imshow(I,RI);
set(gca,'YDir','normal');

Answer 1

[Adam]

doc daspect

[Gerard Capes]

Great, thanks! Easy when you know where to look! I do wonder why it changed the aspect ratio in the first place?

[Adam]

I'm not aware of any overload of imshow that takes an imref2d as 2nd argument. Is this an overload from a toolbox?