(require 'deferred)
(deferred:$
  (deferred:process "wget" "-O" "a.jpg" "http://www.gnu.org/software/emacs/tour/images/splash.png")
  (deferred:nextc it
    (lambda (x) (deferred:process "convert" "a.jpg" "-resize" "100x100" "jpg:b.jpg")))
  (deferred:nextc it
    (lambda (x)
      (insert-image (create-image (expand-file-name "b.jpg") 'jpeg nil)))))