1. A device for extracting pattern features from a streaked pattern having a multiplicity of streaks at least on a fragmentary area thereof, a first plurality of streaks of said multiplicity of streaks having a second plurality of feature points having at least one predetermined relationship to said first plurality of streaks, said device comprising means for two-dimensionally scanning said streaked pattern in synchronism with a timing signal sequence to produce a sequence of picture element signals representative of said streaked pattern, means responsive to said picture element and said timing signal sequences for thinning said multiplicity of streaks generally to skeltons with a background area interposed between two adjacent skeltons to thereby convert said streaked pattern to a skelton pattern comprising skelton points representative of said skeltons and the background areas and to produce a sequence of skelton signals representative of the respective skelton points, feature point extracting and position detecting means responsive to said skelton and said timing signal sequences for extracting said feature points from said skelton points and for detecting positions of the extracted feature points in said skelton pattern, by the use of a skelton signal representative of each skelton point and with reference to the skelton signals representative of the skelton points in that first preselected area of said skelton pattern which is contiguous to and surrounds said each skelton point, to thereby produce a sequence of skelton signals representative of the detected positions, respectively, direction detecting means responsive to said position and said skelton signal sequences for detecting directions defined for the extracted feature points in relation to the skeltons into which said first plurality of streaks are thinned, by the use of a position signal representative of the position of each extracted feature point and with reference to the skelton signals representative of the skelton points in that second preselected area of said skelton pattern which is contiguous to and surrounds in said skelton pattern the skelton point extracted as said each extracted feature point, to thereby produce a sequence of direction signals representative of the detected direction, respectively, and relationship detecting means responsive to said position and said direction signal sequences for detecting a density for each extracted feature point selected as a reference feature point and a plurality of counts for said reference feature point, said density being determined by those of said extracted feature points which have positions in a predetermined area contiguous to and surrounding the position of said reference feature point and are selected as adjacent feature points, each count being related to the number of skeltons intervening between said reference feature point and a related feature point that is nearest to said reference feature point of the extracted feature points having positions in each of a prescribed number of divisions of said skelton pattern, whereby the detected positions, the detected directions, the densities detected for the respective reference feature points, and the counts detected as relationships for the respective reference feature points are extracted as said pattern features.