An image capture and processing system supports a multi-tier modular software, and plug-in extendable, architecture. The image capture and processing system can be realized as an image-capturing cell phone, a digital camera, a video camera, mobile computing terminal and portable data terminal (PDT), provided with suitable hardware platform, communication protocols and user interfaces. A third-party customer can write and install a software plug-in into the application layer so as to enhance or modify the behavior of the image capture and processing system without any required knowledge of the hardware platform, communication protocols and/or user interfaces.