1. An image processing apparatus configured to manage documents, said image processing apparatus comprising: a memory configured to store an instruction; and a processor configured to execute said instruction, said processor being further configured to: generate a first additional image based on an image in a designated region of a first document, generate a second additional image showing a difference between said first document and a second document, said second document being a revision of the first document; and register said first additional image and said second additional image on another device in association with a marker image indicating a revision stage of said first document.