Finding homography with FLANN-based matches

First of all, what is homography? Let's read a definition from the internet:

"A relation between two figures, such that to any point of the one corresponds one and but one point in the other, and vice versa. Thus, a tangent line rolling on a circle cuts two fixed tangents of the circle in two sets of points that are homographic."

If you – like the authors of this book – are none the wiser from the preceding definition, you will probably find the following explanation a bit clearer: homography is a condition in which two figures find each other when one is a perspective distortion of the other.

First, let's take a look at what we want to achieve so that we can fully understand what homography is. Then, we will go through the code.

Imagine that we want to search for the following tattoo:

Figure 6.16: An anchor tattoo, to be used for keypoint matching and finding homography

We, as human beings, can easily locate...