So how can you stop pixels from tracking your movements on the web? I highly recommend Ghostery. It is a FREE browser plugin that by default automatically blocks all trackers and pixels. It is available for Firefox, Safari, Google Chrome, Opera, Internet Explorer, and even iOS. Part of the service is it shows the tracker's company, and allows you to disable/enable blocking of any pixel or tracker.
As of September 16, 2013, Ghostery blocked the this many trackers from the homepage of the following websites:
CNN.com - blocked 11 trackers!
Yahoo.com - blocked 5 trackers!
AllRecipes.com - blocked 7 trackers!
Wikipedia.org - blocked 0 trackers!
In CNN.com's case, your browsing behavior is headed to 11 different companies, who in turn can sell your information to other related companies! But, with Ghostery, this problem is automatically solved.
However, it isn't all positive. Everyone has a different idea of what tracker is considered "bad". For example, Like buttons from Facebook are considered trackers. Everytime you're logged into Facebook and you come across a website with a Like button, you are being tracked by Facebook. Therefore, Ghostery will block the button, which prevents you from "Liking" the website if you're a Facebook user. Luckily, you can "whitelist" Facebook trackers so they always display, or enable one time a Facebook tracker for only the current page. In any event, there is a very easy workaround. This same problem may occur with other online services such as Disqus, Google+, etc...
Important to know, if you don't uncheck GhostRank, Ghostery will annoymously collect your information and sell it back to advertisers. I suggest avoid using the GhostRank feature, something you need to manually uncheck.
In general, I everyone should use Ghostery to block trackers and pixels. It's a very easy set it and forget it way to protect your online privacy.