Had my teenage son help me import jpeg aerial pics of some fields into apex about 4 months ago. I think it took us about 4 hours to search the web and figure out what the world file was and how to make up a file like it.

Kind of fuzzy now in my memory,but i think the world file wants the location of the top left corner of the pic in universal projection ??? or something,and the meters per pixel across the pic.

Not too many lines for the file.but we finally guessed close on the location of the top left corner and then had to use the align or edit feature in apex to finish aligning the pic with a field boundary.Took  a while and only did about 3 or 4 fields.

But they look kind of neat on the GS2 screen in the field. And look even better when printing out yield maps over the aerial pic.

Don't think I can be of any more help than that .....sorry.