Interactive computer based graphics systems are increasingly being used in modelling environments. In these situations the main design goals for software systems, which support visual output display, are: the ease of prototyping, an easy-to-use interface, a large set of graphic primitives and a powerful image composition scheme. This paper first presents the theoretical basis, and then some of the design issues, for a system we built to aid the visualization of the graphical output from a modelling process. The paper concludes by describing applications of the software in various modelling contexts. The main contribution of our research is that it introduces new and powerful image composition techniques as opposed to providing geometric primitives. The graphical output of any formal mathematical model can be described in terms of either an iterated function system, or a recursive function. We have, in our research, used the recursive function approach to describe graphical objects. This is achieved by creating a context free grammar to describe any recursive function. A picture grammar, that is equivalent to the context free grammar, is then developed. The software implementation section of our work focuses on building an interpreter for the resulting language. The main theoretical issues that we deal with in the paper are the design of the recursive functions and context free grammars for visual modelling tools. The main implementation issues that we deal with in the paper are the design of the dynamic data structures, the LOGO-like command nature of the input interface, the context sensitive help system, the design of complex graphic primitives like splines and panelled polygons, and the creation of composite images using the notion of recursive replacement terminating in primitive geometric structures. The current implementation of the tool has been used in several different contexts. Among them are: the modelling of crystal growths, the animation of dynamic processes (for slides in commercials) and the generation of fractal images (to aid in the creative design of wallpaper and textile patterns).