This article outlines the database structure for the MMv4 product_image database table.

• id
  Primary Key of the table.
  int(10) | unsigned | auto increment | primary key | indexed
• pid
  Reference to the product's SID number: product.id.
  int(10) | unsigned | indexed
• display_order
  Determines how the product image is displayed in relation to other images for the same product.
  int(10) | unsigned | indexed
• url
  The URL or path to the largest version of the image file.
  varchar(255)
  
• caption
  The image's caption.
  varchar(255)