1. An optical character reader for detecting frame lines of a character entry frame printed on a medium in which a character is written comprising: scanning means for scanning the medium to produce a bit-mapped image of the medium including a character entry frame image represented with black pixels; frame width determining means for determining a width of the frame lines of the character entry frame based on a histogram of the number of black pixels continuously arranged over one of the frame lines in a direction perpendicular to the one of the frame lines; and frame line equation defining means for defining line equations representing side boundaries of each of the frame lines according to a least-squares method using set of pixels arranged on sides of each of the frame lines over the width of the frame lines determined by said frame width determining means to determine locations of the frame lines on the bit-mapped images.