We discuss the interface of VISTO, a Content Based Image Retrieval system for vector images in SVG (Scalable Vector Graphics) format. The system includes different engines and one common graphical interface. In fact, to support the different requirements of different application domains, the system offers a variety of engines. Most notably, due to its modular architecture, the system allows users to add engines at runtime; the interface provides support for newly added engines, including parameter tuning. The interface is designed for two classes of users: application domain users and researchers in the field of multimedia. Application domain users can use both query-by-sketch and query-by-example to search collections; researcher users can test, tune, and compare engines, and they can design datasets to be used in batch mode. VISTO is an open source project developed in Java; it uses advanced features of the language, such as the Core Reflection API, to dynamically adapt the interface to the available engines. The system is being validated in different application domains, including the production of 2D animation, the Sign Writing Language, and the BLISS Language.