A new progressive image transmission scheme in the spatial domain is developed. The proposed scheme is demonstrated to be applicable to many interactive image communications. The progressive transmission of images could solve the problems related to the lengthy time required to transmit high-resolution images over low-speed channels. The proposed scheme is required to be computationally simple but result in a bit rate improvement. This technique is also demonstrated to be capable of developing operators such as a selective fill-in function. This scheme has encoded an approximate binary image, initially using context-free encoding. The approximate binary image is represented by two lists of identical elements maintained by both sides of the communication, with each list recording the locations of regions of homogeneous intensity. The dynamic thresholding technique is then applied to progressively refine the image. The dynamic threshold is defined as the mean of intensities for each stage. The original list is partitioned by the thresholdings. The information required for updating the lists is compressed by both the prefix coding and the runlength coding. An image can be progressively refined in the future because both sides of the communication maintain the locational lists of the same content. Several computer simulations using the proposed scheme and the bit-plane method are used to illustrate the advantages of the proposed scheme, which is confirmed by performance comparisons to obtain a better result than the bit-plane method.