In　image　registration　or　image　matching,　the　feature　extracted　by　using　the　traditional　methods　does　not　include　the　depth　information　which　may　lead　to　a　mismatch　of　keypoints.　In　this　paper,　we　prove　that　when　the　camera　moves,　the　ratio　of　the　depth　difference　of　a　keypoint　and　its　neighbor　pixel　before　and　after　the　camera　movement　approximates　a　constant.　That　means　the　depth　difference　of　a　keypoint　and　its　neighbor　pixel　after　normalization　is　invariant　to　the　camera　movement.　Based　on　this　property,　all　the　depth　differences　of　a　keypoint　and　its　neighbor　pixels　constitute　a　local　depth-based　feature,　which　can　be　used　as　a　supplement　of　the　traditional　feature.　We　combine　the　local　depth-based　feature　with　the　SIFT　feature　descriptor　to　form　a　new　feature　descriptor,　and　the　experimental　results　show　the　feasibility　and　effectiveness　of　the　new　feature　descriptor.