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Extended Snobol picture pattern processor (ESP3) is a programming language and pattern recognition system which was designed for generating, recognizing, and manipulating two-dimensional line drawings. An ESP3 picture pattern describes a class of line drawings just as a Snobol pattern describes a class of strings. During pattern matching, a subject picture is searched for the occurrence of a sub-picture which matches a given picture pattern. The search of the subject picture is ordered left-to-right and top-to-bottom, and the search program uses scanner guidance information found in the picture pattern to limit the area of the subject picture to be searched. An experimental implementation of ESP3 has been developed to test the feasibility of the system. This paper describes the ESP3 picture patterns, the pattern matching operation, and the experimental implementation of ESP3.