The following code can help replace central portion of a larger image (uniform background) with another smaller (actual image).
%Using an example to solve the problem
B = imread('cameraman.tif');
A = zeros(512,'like',B);
% Assuming large image is A
szA = size(A);
% Assuming smaller image is B
szB = size(B);
centerA = floor(szA(1:2)/2+1);
centerWindow = floor(szB(1:2)/2+1);
offset = centerA - centerWindow + 1;
R = offset(1);
C = offset(2);
H = szB(1);
W = szB(2);
% Replace central portion of larger image with the smaller one
A(R:(R+H-1),C:(C+H-1),:) = B;
% Display the new image
imshow(A)
This can be converted into a function which can be passed the background and central image as parameters. This function can then be called in a loop to automate the entire process.
Hope this helps.
