Google App Engine - PHP App Images/CSS not found

I'm building my first app using Google App Engine and have hit a problem straight off: My images and css are not loading with the error: Failed to load resource: the server responded with a status of 404 (Not Found). I have done all I can think of to try and tackle it, and now I'm stumped. Here's my code:

PHP:

<?php
    echo "<html><header><link rel='stylesheet' type='text/css' href='/stylesheets/style.css'></header>
    <body>
        <div class=header><img src='/images/logo.png'>
        </div><div class=main>hello</div>
    </body></html>";
?>

app.yaml:

application: phpunionapp
version: 1
runtime: php
api_version: 1
threadsafe: yes

handlers:
- url: /favicon\.ico
  static_files: favicon.ico
  upload: favicon\.ico

- url: /images
  static_dir: static/images

- url: .*
  script: main.php

- url: /stylesheets
  static_dir: stylesheets

Directory Structure:

phpunionapp\images\logo.png
phpunionapp\stylesheets\style.css

And the log:

2013-10-13 16:53:01 Running command: "[u'C:\\Python27\\pythonw.exe', 'C:\\Program Files (x86)\\Google\\google_appengine\\dev_appserver.py', '--skip_sdk_update_check=yes', '--port=10080', '--admin_port=8002', u'C:\\Users\\User\\Documents\\Web Development\\Tests\\phpunionapp']"
INFO     2013-10-13 16:53:03,480 devappserver2.py:660] Skipping SDK update check.
INFO     2013-10-13 16:53:03,520 api_server.py:138] Starting API server at: http://localhost:54192
INFO     2013-10-13 16:53:03,523 dispatcher.py:168] Starting module "default" running at: http://localhost:10080
INFO     2013-10-13 16:53:03,526 admin_server.py:117] Starting admin server at: http://localhost:8002
INFO     2013-10-13 16:53:11,661 module.py:599] default: "GET / HTTP/1.1" 200 191
INFO     2013-10-13 16:53:11,713 module.py:599] default: "GET /images/logo.png HTTP/1.1" 404 -
INFO     2013-10-13 16:53:11,844 module.py:599] default: "GET /stylesheets/style.css HTTP/1.1" 200 191

The 404 in the browser:

Failed to load resource: the server responded with a status of 404 (Not Found) http://localhost:10080/images/logo.png

I am honestly not sure why the app cannot find the images, any help would be very much appreciated! Thanks in advance.

In your app.yaml, change static_dir: static/images to static_dir: images.

I got there by noticing in the logs that the stylesheet was getting served, but the image wasn't. That led back to a difference in app.yaml that I'd missed on first look.