Self-fractional Fourier images (SFFIs), which are invariant under the two-dimensional fractional Fourier transform, are considered. Necessary and sufficient conditions for an image to be a SFFI for given angles are formulated. An optical procedure for synthesizing SFFIs from a generator image is developed. The physical meaning of SFFI synthesis is discussed. An image decomposition on the set of orthogonal SFFIs, which simplifies image processing in fractional FT optical systems, is proposed.