.png Images correlation

I am asked to do the correlation with two png images, but i can not do it using corr2() function, any can help me ,, with the code plz ?

Answer 1

[Image Analyst]

Radiometric, or spatial? If radiometric, try psnr() - a common alternative for comparing images, for example a compressed/decompressed image with an original, never-compressed version. If spatial, try xcorr2() or normxcorr2().