The Filename
The name of the world file is based on the raster file's name.
One convention is to append the letter "w" to the end of the raster filename: falknermap.jpg → falknermap.jpgw.
An alternative naming convention is also honored, and in fact is more widespread. The second letter of the original filename extension is removed, and the letter "w" is added at the end. For example, falknermap.jpg → falknermap.jgw or falknermap.tif → falknermap.tfw. This convention was developed for filenames that need to conform to the 8.3 file naming convention.
Read more about this topic: World File