legal ground
Article 27 of the Patent Law of People's Republic of China (PRC)
To apply for a patent for design, a request, a picture or photograph of the design, a brief description of the design and other documents shall be submitted. The relevant pictures or photographs submitted by the applicant shall clearly indicate the design of the product for which patent protection is required.
Article 28
The date when the patent administrative department of the State Council receives the patent application documents is the filing date. If the application documents are mailed, the postmark date of mailing shall be the application date.