No one told me that image spoiling was not working.

4chan_x.user.js

@@ -1676,6 +1676,7 @@
         sub: reply.sub,
         com: reply.com,
         upfile: reply.file,
+        spoiler: reply.spoiler,
         mode: 'regist',
         pwd: (m = d.cookie.match(/4chan_pass=([^;]+)/)) ? decodeURIComponent(m[1]) : $('input[name=pwd]').value,
         recaptcha_challenge_field: challenge,

script.coffee

@@ -1244,14 +1244,15 @@ qr =
       watcher.watch threadID
 
     post =
-      board:  g.BOARD
-      resto:  threadID
-      name:   reply.name
-      email:  reply.email
-      sub:    reply.sub
-      com:    reply.com
-      upfile: reply.file
-      mode:   'regist'
+      board:   g.BOARD
+      resto:   threadID
+      name:    reply.name
+      email:   reply.email
+      sub:     reply.sub
+      com:     reply.com
+      upfile:  reply.file
+      spoiler: reply.spoiler
+      mode:    'regist'
       pwd: if m = d.cookie.match(/4chan_pass=([^;]+)/) then decodeURIComponent m[1] else $('input[name=pwd]').value
       recaptcha_challenge_field: challenge
       recaptcha_response_field:  response