While this relies on the continued existence of the codecogs website, the countervailing advantage of this method is that the LaTeX input statement used to generate an equation becomes embedded in the web page. For example, if you look at the source of this web page, you will see that the above equation for the derivative of the natural logarithm is generated using this statement:
\frac{d}{dx}\ln(x)=\frac{1}{x}
Should codecogs cease to exist, the LateX input statement has been preserved and may be used with any converter to regenerate the typeset image. As for LaTeX itself, it is one of those Unix things that has been around for 30 years and is now distributed under the LaTeX Project Public License.
Des.de.mona
