1. An image processing apparatus which is accessible to at least one storage device storing a shelf image acquired by photographing, by a first camera, a display shelf for displaying a product, and an single item image acquired by photographing the product as a single piece with a known photographing distance, the apparatus comprising: a decision unit configured to estimate a separation distance from the first camera to the display shelf, and to decide a search distance, based on the separation distance; a generation unit configured to generate a template image by converting a number of pixels of the single item image stored in the storage device, with a magnification corresponding to a ratio between the search distance decided by the decision unit and the known photographing distance; and a determination unit configured to determine an area, which is similar to the template image, within the shelf image captured by the first camera and stored in the storage device.