You need OEM image, and from a particular manufacturer. Not all manufacturers provide it. When you purchase the laptop attached or ROM distribution (for earlier models) or a recovery drive (installed system in factory state) or the installed utility to create this disk from a hidden partition on hard (the last time the most frequent case). Technical support may (but not obliged) to send you a disk if you would make her. Good people sometimes post these images to the trackers, ftp and other places. So look on the forums in topics that discuss this model.
As for the legality, downloaded from somewhere in the image, and then and installing it unfortunately will not be fully legitimate from the point of view of the legislation of the Russian Federation, despite the presence of the key. Although you claim no one produces, because after installation it is impossible to determine from which was taken the distribution. (If interested in details, read on iXBT, there, the issue was chew repeatedly.)