One recent entry into the free pornography website market are Thumbnail gallery post sites.
These are free websites that post links to commercial sites, providing a sampling of the commercial site in the form of thumbnail images, or in the form of Free Hosted Galleriessamplings of full-sized content provided and hosted by the commercial sites to promote their site.
While the study's authors note this increase is "smaller than conventional wisdom might predict," it's still quite significant.
There are several forms of sites delivering adult content. The most common form of adult content is a categorized list (more often it's a table) of small pictures (called "thumbnails") linked to galleries.
On the Web, there are both commercial and free pornography sites.
The bandwidth usage of a pornography site is relatively high, and the income a free site can earn through advertising may not be sufficient to cover the costs of that bandwidth.
This type of distribution was generally free (apart from fees for Internet access), and provided a great deal of anonymity.
The anonymity made it safe and easy to ignore copyright restrictions, as well as protecting the identity of uploaders and downloaders.