how to do image decryption using RSA alogrithm?

i tried this code for decryption of image using RSA algorithm. I'm not getting the original image back.

 for i=1:x
    for j=1:y
       P(i,j)= mod((C(i,j)^d),n);  
   end
end
figure(3);
imshow(P);

where C is the encrypted image

please help.