The traditional TeX82 outputs device independent (DVI) files, which as the name implies, are intended to be independent of the output device, but do not embed the actual fonts. As such, DVI files are not suitable for use by web browsers, and a conversion program is needed to translate from a DVI file to an image. Dvipng renders the font glyphs into the images, for example using FreeType when available.
Although it is possible to generate web graphics using other DVI backends such as dvips followed by a PostScript-to-image converter like ImageMagick, using dvipng requires fewer programs to be run. Dvipng is used as the default rendering method for MediaWiki software, as of version 1.8.0. It is also included in the TeXLive distribution and several Linux distributions.
Dvipng is released under the GNU LGPL.