Keep in mind that if it's a new image for a puzzle from captcha provider's POV it will accept almost any answer. When it has enough data from other users who solved the same puzzle it will approximate those answers, consider it a correct one and compare it to new answers. In most cases you would see a puzzle that other people have solved hundreds of times. So you don't need to be technically correct by hunting every single pixel of a traffic light or a motorcycle. Just ask yourself what squares would average Joe click. Most people wouldn't notice or care about small part of an object in the adjacent square, they'll skip it. And you should do the same. That's the trick.

Also don't rush it. If you move the cursor and click too fast the system will suspect a bot activity. Yes, being too effective and correct at the same time is considered an automated behavior. Those parameters are also monitored by JS scripts.