GDAL, Georeferencing

I have been trying to use GDAL library to add geoinformation to an image. From the documentation from GDAL web page I could find that I could use GDAlSetGeotransform(), for that I need a six parameters GDAL transformation information. Among the six parameters, the x-rotation and y rotation are considered 0 for north up image. But in my case I don’t have north up image. So how could I get these rotation values if I have four corner coordinates of the image.
Or there is any other technique to add geoinformation to my image if I have four corner coordinates of the image.