How to compute psnr of original lena image and watermarked lena image?

The attached code is used for embedding and extraction of digital watermark on the cover image by extracting its feature points. I wish to compute the psnr value of lena image and watermarked lena image.As per the research paper ,the computed psnr value of watermarked lena image is 38.9119. But when i am calculating psnr value i am getting the value to be 49.5156 using peaksnr = psnr(A,ref) command. can anybody tell me any other method so that i can get the desired psnr value. Attaching code for watermarking and test images required.