how to overlay the image on the surface?

i want to overlay an image on the generated surface (which we generate by algorithms)

the problem is that when we try to overlay the image on generated surface, the result is coming but when i execute it again without the surface code the result is still same. i don't understand where this generated surface is getting saved so image automatically comes in that shape.

% make dummy test data%
N = 400;
X = 1:N;
Y = 1:N;
[X, Y] = meshgrid(X,Y);
Z = (X+Y)/20;
%mesh(Z);
%colormap(red);
%surf(X,Y,Z);
%axis([0 10 0 10 0 40]);

% read jpg and make same size as grid    
im = imread('cameraman.tif');
% convert image to indexed colours    
[im, map] = rgb2ind(im, 256);

% make figure
figure(1),clf

% make image same size as grid
subimage = im(1:N,1:N);
colormap(map)

% plot surf and use image as texture
s = surf(X,Y,Z);
set(s, 'faceColor', 'texture',...
    'edgecolor', 'none',...
    'cdata', subimage)