%this draws rectangle on top of I1
subplot(1, 2, 1); % Focus is with axes #1.
imshow(I1, [])
rectangle('Position',[x,y,w,h])
%somewhere else after the above code
%this draws the rectangle on top of I2
subplot(1, 2, 2); % Focus is with axes #2.
imshow(I2, [])
rectangle('Position',[x,y,w,h])
% Back to #1 now.
%this draws rectangle on top of I1
subplot(1, 2, 1); % Focus is with axes #1.
rectangle('Position',[x,y,w,h])