width(img)
  return image-size(img)[0]

height(img)
  return image-size(img)[1]

body
  foo image-size('gif')
  foo image-size('gif')[0] == width('gif')
  foo image-size('gif')[1] == height('gif')

body
  foo image-size('tux.png')
  foo image-size('tux.png')
/*
body
  foo image-size('jpeg')