Wireless networks in combination with image sensors open up a multitude of previously unthinkable sensing applications. Capable tools and testbeds for these wireless image sensor networks can greatly accelerate development of complex, yet efficient algorithms that meet application requirements. In this paper, we introduce WiSNAP (Wireless Image Sensor Network Application Platform), a Matlab-based application development platform intended for wireless image sensor networks. It allows researchers and developers of such networks to investigate, design, and evaluate algorithms and applications using real target hardware. WiSNAP offers standardized and easy-to-use Application Program Interfaces (APIs) to control image sensors and wireless motes, which do not require detailed knowledge of the target hardware. Nonetheless, its open system architecture enables support of virtually any kind of sensor or wireless mote. Several application examples illustrate the usage of WiSNAP as a powerful development tool.