WLD -- ESRI World File
A world file file is a plain ASCII text file consisting of six values separated by newlines. The format is:
pixel X size rotation about the Y axis (usually 0.0) rotation about the X axis (usually 0.0) negative pixel Y size X coordinate of upper left pixel center Y coordinate of upper left pixel center
60.0000000000 0.0000000000 0.0000000000 -60.0000000000 440750.0000000000 3751290.0000000000
You can construct that file simply by using your favorite text editor.
World file usually has suffix
.wld, but sometimes it may has
.jgw or other suffixes depending on the image file it comes with.