In the practical transmission of compressed still images, bit errors may occur, which probably result in desynchronization and packet loss. In packet-switched networks, network congestion also results in packet loss. This survey article reviews the error resilience factors that must be faced by a robust image encoder and decoder (codec). The article begins with the enumeration of the different kinds of impact noisy channels and congested networks have on block-coded images. Then we present different techniques that can be applied to combat the degradation of the images introduced by the noisy channel and network congestion. These techniques include resynchronization strategies, post-processing error concealment algorithms, and preprocessing error control techniques. All these techniques can be either used directly or extended to robust video transmission.