A Selective Dropping Congestion Control (SDCC) algorithm is proposed in this work, for wireless multimedia sensor networks based on scalable multimedia encoding. SDCC, which has been designed by means of linear discrete time control theory arguments, can be applied in a fully distributed way. It periodically evaluates at each node the amount of data to drop, in order to control the level of the transmission queue, and then selects the packets to discard based on their relevance to the image quality. SDCC effectiveness has been evaluated with reference to a video-surveillance problem in several scenarios, using the Castalia simulator. Results have shown that SDCC is able to significantly improve the network performance in terms of image delivery ratio and delay.