mapping x-y coordinates of image to lattitude longitude from four corner lattitude longitude

Question

Hi All,
I have custom map image with specific height and width.
i need to map x-y coordinates of image to lattitude longitude from four corner lattitude longitude available.
 
this requirement is for fulfill current location of user into custom image map.
 
more on this on image i have specific few points on image, based on current position of user, i need to find near by point on image.
 
Thanks in advance.