Provided is an image sensor including a substrate, in which a pixel area including a plurality of unit pixels, an optical black area located outside of the pixel area, and an alignment key area located outside of the pixel area are included, the substrate having a first surface and a second surface opposing the first surface, an interconnection structure below the first surface of the substrate, photoelectric conversion elements in the pixel area of the substrate, an insulating layer on the second surface of the substrate, a grid layer on the insulating layer in the pixel area and the alignment key area, a key pattern layer between the insulating layer disposed in the alignment key area and the grid layer disposed in the alignment key area, the key pattern layer including a protruding region to correspond to the grid layer, and color filters on the insulating layer and the grid layer in the pixel area.