A method for encoding characters includes identifying one or more sequences of the character codes that are likely to be generated due a segmentation error in application of a pattern recognition process, and associating a respective extension character code with each of the sequences. The area of an image containing characters is divided into segments, such that each segment contains approximately one character. The pattern recognition process is applied to each of the segments in order to generate an input string of character codes. At least one of the identified sequences of the character codes in the input string is replaced with the respective extension character code so as to generate a modified string. The output string is determined by comparing the modified string to a directory of known strings.