1. An image processing apparatus, for editing a parameter of extracting a region which is in association with a real space object from a real image, with visualization of both a border line of a virtual mask image and a border line of the real space object on the real image, the image processing apparatus comprising: an image acquisition unit configured to acquire a real image obtained by capturing the real space object; a region extraction unit configured to extract a region which is associated with the real space object from the real image, using an extraction parameter which is set in advance; a generation unit configured to generate a translucent virtual mask image based on a transparency parameter; a combining unit configured to generate a composite image of the real image and the translucent virtual mask image, wherein the translucent virtual mask image has been clipped based on the extracted region; a display unit configured to display the composite image; and a changing unit configured to change the extraction parameter based on an input operation, after displaying the composite image by the displaying unit.