中文说明：
Hu的七个不变矩在图像匹配检索中适用广泛。本代码仅计算图像间Hu的七个矩的D2大小，直观的了解Hu矩的应用。
English Description：
Hu's seven invariant moments are widely used in image matching and retrieval. This code only calculates the D2 size of the seven moments of Hu between images to intuitively understand the application of Hu moments