The Sobel and Sharr first derivative operators are to be used to take the x and y derivatives of an image. Then a small region of interest (ROI) is to be defined to detect corners in.
A 2x2 matrix of sums of the x and
y derivatives is created as follows: 
Solving
where
λ is
a column vector of the eigen values and I is
the identity matrix, gives the eigen values. For the 2x2
matrix of the equation above, the solutions may be written in closed
form: 
If λ1, λ2 > t, where t is some threshold, then a corner is considered to be found at that location. This can be very useful for object or shape recognition.