I'm a newbie to the world of Computer Vision. Here's what I need to do. Given an image, pick out and draw a circle around all the locations in the image which contain an object A. In other words, say there are 3 darts on a shooting board and I want to return the locations of them. How would I do this using OpenCV? What's the name of the technique(s) I would have to use. I want to know what parts of the library to get familiar with in order to implement this feature.
So this tutorial seems to cover some of the basic topics. You should look for pattern recognition, edge detection... I do not know if you will be working with static images, or video. A mix of techniques can be combined, and the robustness of the method depends on how much time you can spend processing the given image/frame.
To draw stuff on the image its pretty simple, for example a circle is a simple function call with a few parameters.
I am no expert in this matters, but I'd you can start with a static image and draw some circles, then look for a way to detect your pattern (for example, to extract image properties you can look into SURF)
Also if you have access to Matlab, it can perform some image processing.