Pattern Matching - Find reference object in second image [OpenCV?]

Question

I have a reference b/w image that contains a reference object (a coin for example). The object is marked by the user, that is the region of interest.

Now I want to

Answer 1

The question is quite broad and there are many ways depending on what exactly you want to achieve. You can use the Hough Transform to detect the coin because it's round, though it might detect many round elements (so it depends on whether you have other similar things in view).

More generally, you need to use feature detector (SURF, ORB, FAST, Shi-Tomassi), do extraction and matching between a reference frame that has the coin and the frame in which you're looking for it. Then, you can use the Homography Transform to ensure that the points you've found are the same, and hence you've found your coin.

Take a look at this example:

Features2D + Homography to find a known object