Abstract: State-of-the-art OCR/ICR algorithms and software are the result of large-scale experiments on the accuracy of OCR systems and proper selection of the size and distribution of training sets. The key factor in improving OCR technology is the degradation models. While it is a leading-edge tool for processing conventional printed materials, the degradation model now faces additional challenges as a result of the appearance in recent years of new imaging media, new definitions of text information, and the need to process low quality document images. In addition to discussing these challenges in this paper, we present well-developed degradation models and suggest some directions for further study. Particular attention is paid to restoration and enhancement of degraded single-sided or multi-sided document images which suffer from bleed-through or shadow-through.