Recently, VSNs (Visual Sensor Networks) are becoming of increased interest in a variety of applications. Due to power constraints at each visual sensor node, the processing of live video is constrained. In this paper, we propose a DCT (Discrete Cosine Transform)-based bit allocation scheme to maximize image quality for a given bit rate constraint. Two major featured algorithms are proposed : "SLO" (Searching from the Lowest Order) and "SPP" (Searching the Present optimal bit allocation from the Previous optimal bit allocation). The proposed algorithms reduce the search range based on a simple IQA (Image Quality Assessment) model and DCT statistics. Thus, they demonstrate low-complexity and fast computation. In the simulations, we show the superiority of the proposed algorithms over conventional approaches.