This paper describes a massively parallel dataflow computer dedicated to real-time image processing. Two types of data-driven processing elements are embedded into a regular cubic mesh: 1024 low level custom dataflow processors (50Mops/s each) and 36 T800 transputers. The programming environment relies on an extensive use of the functional programming (FP) concept. An image processing algorithm first expressed in an FP-like functional syntax is converted into a dataflow graph, the nodes of which are real-time operators to be implemented on physical processors by direct mapping onto the array. The concepts and the architecture, both hardware and software, are explained in detail. We conclude with an example of a complete implementation: a connected components labeling working in real time.