Extracting secret image from cover image I want to develop a steganography project with using exploiting modification direction method. I started to try and understand how the method works, but I have some questions about decryption.

I hid the secret image in a cover image larger than the secret image by 9 times. So when it comes to decryption I'm not going to use all of the pixels of the cover image: I only need to use those pixels used during encryption. But if the pixel count isn't provided before then how can I know how many pixels should be used to extract the secret image?

If I use all pixels of the cover image the resulting image's size doesn't match the original one and it is quite likely there will be flaws in the 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The EMD method is a little outdated.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.