I don't think the scaling has to be perfect, if you use the "align feature" in apex. In other words choose at least three points on your map and the same number of points on your pic. They should represent the same points on both,then align and apex should match them up pretty close.

The last two lines on the jgw file are UTM coordinates of the top left corner of your pic. You could go on google earth to see what that would be in latitude and longitude. Then use the converter calcuator to get the UTM(universal transverse mercator)coordinates.