The retrieval of images based on their visual similarity to an example image is an important and fascinating area of research. Here, we discuss various ways in which visual appearance may be characterized for determining both global and local similarity in images. One popular method involves the computation of global measures like moment invariants to characterize global similarity. Although this means that the image may be characterized using a few numbers, the performance is often poor.
Techniques based on moment invariants often perform poorly.
They require that the object be a binary shape without holes which is often not practical. Image Retrieval by Appearance - Ravela, al. On computing local and global similarity in images. SPIE conf. on Human and Electronic Imaging III,, 1998. On computing local and global similarity in images.