Xiang, F., H. Yong, S. Dandan, and Z. Jiexian. “An Image Retrieval Method Based on Hu Invariant Moment and Improved Annular Histogram”. Elektronika Ir Elektrotechnika, vol. 19, no. 10, Mar. 2013, pp. 114-8, doi:10.5755/j01.eee.19.10.3925.