1. A method for registering images, comprising: acquiring a reference image; acquiring a moving image; calculating an initial degree of registration between the reference and moving images; calculating a gradient field for the reference image; generating an incremental deformation based on the calculated gradient; calculating a second degree of registration between an incrementally deformed reference image and the moving image; determining whether the second degree of registration is greater than the initial degree of registration; when the second degree of registration is greater than the initial degree of registration, applying an inverse of the incremental deformation to the moving image; determining whether a second degree of registration is maximized, wherein a similarity function is used to determine whether the second degree of registration is greater than the initial degree of registration and to determine whether the second degree of registration is maximized, wherein the similarity function is optimized uses the equation: { ϕ * = ϕ 0 · δ 1 - 1 · δ 2 - 1 · … · δ ∞ - 1 ϕ k = id + ɛ ⁢ ∂ ∂ δ ⁢ S ⁡ ( I 1 · δ , I 2 · ϕ 0 · δ 1 - 1 · δ 2 - 1 · … · δ k - 1 - 1 ) ⁢ | δ = id wherein ε>0 is sufficiently small to provide for the invertibility of δ k , id denotes the identity of mapping and δ ∞ represents δ n for a value n sufficiently large to attain convergence criteria.