Extracting secret image from cover image
The EMD method is a little outdated. The state of the art are Syndrome Tellis Codes. Please, check:

http://dde.binghamton.edu/filler/pdf/Fill10tifs-stc.pdf

In the EMD method, n pixels are used to carry one secret digit. Therefore, to extract this digit you need to use the same n pixels. The receiver needs to know what pixels are used by the sender.