The review summarizes basic problems of the computer representation of graphic images of the structures of organic compounds. All principal methods, from linear notations (WLN) to topological representation, are covered. Main features of the methodology of usage are described on examples from the most important structure information sources, REGISTRY of Chemical Abstracts and Beilstein's "CrossFire". Some other structure and reaction databases are also listed. The problems and methodology of access to such information sources in local-network environment or of connection to distant database vendors are discussed in detail. It is stressed that so called "flat-fee" payment policy, which gives an unlimited access for staff members of subscribing institutions or students at universities, is the best way for the really efficient and productive exploitation of structure and reaction databases.