This paper presents an overview of methods for recognition of omnifont printed Roman alphabet characters with various fonts, sizes and formats (plain, bold, etc.) from OCR system perspectives. First, it summarizes the current needs for optical printed character recognition (OPCR) in general, and then describes its importance for conversion between paper and electronic media. Current status of commercially available software and products for OPCR are briefly reviewed. Analysis indicates that the challenge we face in OPCR is far from being solved, and there is still a great gap between human needs and machine reading capabilities. Second, OPCR systems and algorithms are briefly reviewed and compared from the context of digital document processing for the following four stages: preprocessing of images, segmentation, recognition, and post-processing. Finally, possible research directions to improve the performance of OPCR systems are suggested, such as using an approach based on the combination of template matching and varieties of feature-based algorithms to recognize isolated characters, the use of multilayered architectures for OPCR, and parallel processing- based high-performance architectures.