Primitive

-- save in Script Editor as an Application, then
-- drag image files onto the Application's icon
 
on open some_items
  repeat with this_item in some_items
    try
      rescale_and_save(this_item)
    end try
  end repeat
end open
 
to rescale_and_save(this_item)
  tell application "Image Events"
    launch
  set the target_width to 120
 
  -- open the image file
  set this_image to open this_item
 
  set typ to file type of this_image
 
  copy dimensions of this_image to {current_width, current_height}
  if current_width is greater than current_height then
    scale this_image to size target_width
  else
    -- figure out new height
    -- y2 = (y1 * x2) / x1
    set the new_height to (current_height * target_width) / current_width
    scale this_image to size new_height
  end if
 
  tell application "Finder" to set new_item to (container of this_item
      as string) & "scaled." & (name of this_item)
    save this_image in new_item as typ
  end tell
end rescale_and_save

set the target_width to 120