Added Harris detector (#34)

Author: GreatestCapacity

Image Processing/Harris Detector.md

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+# Harris Detector
+
+## Problem Statement
+
+Detect corners and edges in a given image.
+
+## Approach
+
+Given image $I$, $n\times n$ size Gaussian Kernel $G_{n\times n}$,
+
+1. Compute the gradients of the image, both horizontal and vertical directions. $X=(-1, 0, 1)\otimes I$, $Y=(-1, 0, 1)^T \otimes I$
+2. Compute the matrix $M$, where $A = G_{n\times n} \otimes X^2$, $B=G_{n\times n}\otimes Y^2$, $C=G_{n\times n}\otimes XY$
+3. Compute the response function $R$, where $R=AB-C^2-k(A+B)$
+4. Classify all points in $R​$.
+
+## Code Implementation Links
+
+- [Python](https://github.com/TheAlgorithms/Python/blob/master/digital_image_processing/feature_detectors/harris.py)
+
+## Reference
+
+C. Harris and M. Stephens, “A Combined Corner and Edge Detector,” in *Procedings of the Alvey Vision Conference 1988*, Manchester, 1988, pp. 23.1-23.6.
+