Arrow key navigation in picture captcha.

src/Posting/Captcha.fixes.coffee

@@ -20,18 +20,35 @@ Captcha.fixes =
     $.addStyle "#{@selectors.image}:focus {outline: 2px solid #4a90e2;}"
     @fixImages()
     new MutationObserver(=> @fixImages()).observe d.body, {childList: true, subtree: true}
+    $.on d, 'keydown', @keybinds.bind(@)
 
   fixImages: ->
-    return unless (images = $$ @selectors.image).length
+    return unless (@images = $$ @selectors.image).length
-    focus = images[0].tabIndex isnt 0
+    focus = @images[0].tabIndex isnt 0
-    for img in images
+    for img in @images
       img.tabIndex = 0
-    @focusImage images[0] if focus
+    @focusImage() if focus
 
-  focusImage: (img) ->
+  focusImage: ->
     # XXX Image is not focusable at first in Firefox; to be refactored when I figure out why.
+    img = @images[0]
     $.asap ->
       return true unless doc.contains img
       img.focus()
       d.activeElement is img
     , ->
+
+  keybinds: (e) ->
+    return unless @images and doc.contains(@images[0]) and d.activeElement
+    x = @images.indexOf d.activeElement
+    if x < 0
+      return unless $('.rc-controls').contains d.activeElement
+      x = 11
+    return unless dx = {38: 9, 40: 3, 37: 11, 39: 1}[e.keyCode]
+    if x is 11 and dx is 11 # left from buttons
+      x = 8
+    else
+      x = (x + dx) % 12
+    (@images[x] or $.id 'recaptcha-verify-button').focus()
+    e.preventDefault()
+    e.stopPropagation()