i am working in matlab to embed audio file in an image. but i am having difficulty in reading the maximum area in the original image ?

i have found the max area by applying thresholding n my image is converted into binary image after that i have labeled that binary image and made a mask .then read the area of the mask, with index . now i have to read the area from original image , from mask i am able to know the max area only but as i have to embed my file in original image so i have to read that max area from original image.