I have blended/merged 2 images img1 and img2 with this code which is woking fine.What i want to know is how to obtain the original two images img1 and img2.The code for blending is as under

img1=imread('C:\MATLAB7\Picture5.jpg');
img2=imread('C:\MATLAB7\Picture6.jpg');
for i=1:size(img1,1)
  for j=1:size(img1,2)
    for k=1:size(img1,3)
      output(i,j,k)=(img1(i,j,k)+img2(i,j,k))/2;
    end
   end
end
imshow(output,[0 255]);