"Digital Museum/Library" is an ongoing project sponsored by the National Science Council of Taiwan. The content of this paper is partial result of one of its subprojects called "Image content-based retrieval on a fish database of Taiwan." The objective of this project is to develop an image content-based search engine which can perform identity check of a fish. It is well known that conventional fish databases can only be retrieved by text-based query. In this study we shall use shape, color, and other features extracted from a fish to search the fish database of Taiwan. The developed technique is able to perform scale, translation, and rotation invariant matching between two fishes. Currently, the database contains several hundreds of fishes. In the future, we shall enhance the capability of the search engine to deal with more than 2,000 fish species, which is the total amount of fish species along the coast of Taiwan.