1. A learning device comprising: generating means configured to generate an image having different resolution from an input image; extracting means configured to extract a feature point serving as a processing object from the image generated by the generating means; calculating means configured to calculate a feature amount of the feature point by subjecting the feature point to filter processing employing a predetermined filter; and identifier generating means configured to generate an identifier for detecting a predetermined target object from the generated image by statistical learning employing the feature amount; wherein the predetermined filter includes a plurality of regions, and the calculating means takes a difference value of difference between a first region of the plurality of regions and a second region of the plurality of regions as the feature amount, wherein a size of the first region is different than a size of the second region, and wherein the calculating means execute convolution operation in a differential function of a predetermined order of a Gaussian function in an arbitrary angle to calculate summation of absolute values of operation results.