Yes that's true. You're only calling it on the very last image you read in. If you want a value for every image, put it in the loop and index it.
for i = 1 : length(srcFiles)
filename = strcat('----',srcFiles(i).name);
I = imread(filename);
E(i) = entropy(I);
end
If you want a value for every pixel in the image, use entropyfilt() instead of entropy().
entropyImage{i} = entropyfilt(I);
You can compute PSNR with the Image Processing Toolbox function called psnr().
