A method for maintaining inventory within a store includes: accessing an image (e.g., a color image, depth image) depicting an inventory structure; detecting a slot region of the image depicting a slot; identifying a product type assigned to the slot; accessing a product dimension of the product type; defining a target region within the slot in the image based on the product dimension; defining a product region within the slot in the image based on the product dimension and the target region; defining a back-of-shelf plane intersecting the target region of the image; detecting a surface within the product region; and, in response to the surface intersecting the back-of-shelf plane, identifying the slot as empty and generating a prompt to restock the slot with product units of the product type.