Wireless Sensor Networks (WSNs) are becoming more imperative in monitoring and surveillance applications, such as border surveillance. For these applications, cameras attached on several sensor nodes are placed on preselected locations in the border region. In case of an intrusion event, these cameras capture images and transmit them to the sink node via other sensor nodes. WSNs operate with limited resources. Therefore, resource utilization is needed when processing and transporting images. In this study, we propose a cost-effective method for dynamic (on-the-fly) prioritization of image macro-blocks. Therefore, we employ a simple encoding scheme at the source node by labeling data blocks as "important" and "not-important" based on the information they contain. The network then transmits "important" data blocks from reliable paths. We established an experimental setup to assess the success of the proposed method using various prioritization measures for labeling and we compared the results with JPEG encoding. The results indicate the usefulness of the proposed prioritization based encoding scheme in terms of transferred image quality, delay and energy. (C) 2013 Elsevier Ltd. All rights reserved.