Hi,
This is the basic formula:
It's just a text file based on the file extension of the image e.g. tfw, pgw, etc. Google will help there.
The contents of the file are 6 lines:
5.000000000000 (size of pixel in x direction)
0.000000000000 (rotation term for row)
0.000000000000 (rotation term for column)
-5.000000000000 (size of pixel in y direction)
492169.690845528910 (x coordinate of centre of upper left pixel in map units)
5426523.318065105000 (y coordinate of centre of upper left pixel in map units)
Cheers
Mike