Euclidean distance between two cv::Mat images

edit

I am trying to write code whetre I need to compute Euclidean distance between two images (cv::Mat). Effectively, I'll take difference between corresponding pixels, sum the distances, and divide by the number of pixels. Both frames are of equal dimensions and depth. I could not find a function to do this by my search. I just wanted to confirm that such an inbuilt function does not exist before I write one myself. Can some knowledgeable person confirm that? Or point me to one if it exists?