defined by which type of device is used to compose it. A blog written by a mobile device like a mobile phone or PDA could be called a moblog. One early blog was Wearable Wireless Webcam, an online shared diary of a person's personal life combining text, video, and pictures transmitted live from a wearable computer and EyeTap device to a web site. This practice of semi-automated blogging with live video together with text was referred to as sousveillance. Such journals have been used as evidence in legal matters. Reverse blog A reverse blog is composed by its users rather than a single blogger. This system has the characteristics of a blog and the writing of several authors. These can be written by several contributing authors on a topic or opened up for anyone to write. There is typically some limit to the number of entries to keep it from operating like a web forum. Community and cataloging Blogosphere The collective community of all blogs and blog authors, particularly notable and widely read blogs, is known as the blogosphere. Since all blogs are on the internet by definition, they may be seen as interconnected and socially networked, through blogrolls, comments, linkbacks (refbacks, trackbacks or pingbacks), and backlinks. Discussions "in the blogosphere" were occasionally used by the media as a gauge of public opinion on various issues. Because new, untapped communities of bloggers and their readers can emerge in the space of a few years, Internet marketers pay close attention to "trends in the blogosphere". Blog search engines Several blog search engines have been used to search blog contents, such as Bloglines (defunct), BlogScope (defunct), and Technorati (defunct). Blogging communities and directories Several online communities exist that connect people to blogs and bloggers to other bloggers. Interest-specific blogging platforms are also available. For instance, Blogster has a sizable community of political bloggers among its members. Global Voices aggregates international bloggers, "with emphasis on voices that are not ordinarily heard in international mainstream media." Blogging and advertising It is common for blogs to feature banner advertisements or promotional content, either to financially benefit the blogger, support website hosting costs, or to promote the blogger's favourite causes or products. The popularity of blogs has also given rise to "fake blogs" in which a company will create a fictional blog as a marketing tool to promote a product. As the popularity of blogging continued