## 1 Introduction  
Wireless multimedia sensor networks (WMSNs) are a new and emerging type of sensor networks that contain sensor nodes with capability of obtaining multimedia content such as video and audio streams, still images, and scalar sensor data from the environment [1, 2]. Recently, some new applications for wireless multimedia sensor networks such as multimedia monitoring systems [3], advanced health care delivery [4], automated assistance for the elderly and family monitors [5], traffic avoidance, enforcement, and control systems [6] have appeared. Capturing images from a desired scene is necessary in many monitoring applications. By increasing the field of view and resolution of these images, more applications are realizable. One common way to achieve this goal is to use strong and costly cameras in a single-tier network topology that leads to more energy usage and cost. According to the characteristics of WMSNs, utilizing only these cameras is not acceptable. To have more feasible networks, most applications use different type of camera sensor nodes that are organized in multi-tier topologies. However, available multi-tier topologies have more than two tiers with high cost camera sensors in upper tiers which increases the network cost and complicates the network management. In this paper, a methodology to provide high resolution images with wide field of view in Camera-Based WMSNs is presented that have following contributions: (i) utilizing an image stitching method in WMSNs, (ii) designing a two-tier network topology with new structures which has camera sensor nodes only in lower-tier, (iii) presenting a method that let upper-tier sensor nodes perform a simplified image stitching, and (iv) presenting an innovative algorithm for lower-tier camera nodes to have a good coverage of field for longer time by selecting them fairly. The presented network topology in this paper consists of just two tiers. Unlike common multi-tier WMSN topologies this topology has camera sensor nodes only in its lower-tier. Also, in the other topologies, multiple tiers are equipped with cameras and the capabilities of camera sensor nodes in them increase from lower-tier to Sink. As lower-tier camera nodes are low cost, it is possible to have high density in this tier and consequently highly overlapped coverage. This property which decreases the coverage failure is utilized to provide a suitable coverage for a longer time. The presented network upper-tier includes stronger sensor nodes without camera. This two-tier topology and its intra-tier and inter-tier communication methods have been described in Section 3. Having numerous low-resolution images, provided by many low cost sensor nodes in lower-tier, is not acceptable for many monitoring applications. Therefore, to create a high resolution and wide image, this paper simplifies and utilizes an image stitching method in a specific way which has been adapted to WMSNs constraints. As image stitching procedure requires a lot of processing overhead, the stitching method is distributed between Sink and upper-tier sensor nodes such that Sink performs main steps of methodology like image processing and some specific extracted information is sent to related nodes in the upper-tier by Sink. Having this information, upper-tier sensor nodes are able to perform stitching procedure with low computational overhead in the next times. By stitching images which have overlaps, the size of whole data that must be transmitted hierarchically through upper-tier to Sink decreases. Consequently, as the main reason of energy consumption is data transmission, decreasing the data transmission size prolongs the lifetime of upper-tier. More details about the stitching method are explained in subsection 4.1. Energy consumption is the most important issue in WMSNs. Because the density of camera sensor nodes in the lower-tier is high and areas covered by them have large overlaps, therefore, selecting an appropriate subset of them that provides an acceptable coverage of desired area must be considered.