Adding media to Wordpress via PHP script

Looking for function to be built in which I can pass two parameters (image location on the server, and post ID) and this function would then add the image to the word press media library running on the same server and then set that media as the Featured image for the given post ID. This function needs to use the word press media library so word press will auto generate the various image sizes and keep track of them in it's own back end database. Please let me know if you have any other questions before bidding. Sean