GAE PHP - image (.jpg) file not found on the server

Question

My image file is not found on the server. I declared it as static on my app.yaml:

- url: /sampleimage\.jpg
  static_files: sampleimage.jpg
  upload: sampleimage\.jpg

As you can see it's on the root directory, I tested it first on localhost and it is found:

localhost:8080/sampleimage.jpg

However when deployed on the web it's not there:

http://samplesite.appspot.com/sampleimage.jpg

I don't know what I'm doing wrong here because my favicon.ico which is also static file is working fine http://samplesite.appspot.com/favicon.ico.

complete app.yaml:

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

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

- url: /
  script: index.html

- url: /sampleimage\.jpg
  static_files: sampleimage.jpg
  upload: sampleimage\.jpg