Person Accounts consume a record in both the Account and Contact objects. In Person Account, Account takes 2kb and Contact takes 2kb, so each Person Account record will require 4KB of storage space.
Each record allocates 2KB, so each Person Account record will require 4KB of storage space. As an example, 500,000 person accounts will require 2GB (500,000 * 4KB) of storage. Images from Rich Text Fields are stored in file storage area