Federal law requires the disclosure of vehicle mileage on an odometer disclosure statement when transferring ownership on a motor vehicle 9 years old and newer. Odometer disclosure statements must have a secure printing process. Disclosures must show on the certificate of title or on a separate secure odometer disclosure form
Notarized signatures of all registered owners to be shown on the new title
Since a title transfer requires a notarized or certified signature of the new owners, it is not possible to process these on the Internet.
References
Washington State Department of Licensing - Titles
Washington State Department of Licensing - Buying or selling a vehicle
Washington State Department of Licensing - Use Tax