Insertamos una imagen y en la URL escribimos:
http://www.codecogs.com/gif.latex?x^2
Obtenemos: 
Si escribimos:
http://www.codecogs.com/gif.latex?\displaystyle \int_\Omega f(x)dx
Obtenemos:

Segundo Método
Usando Mathjax.
Para ello, según dice la documentación, tenemos que modificar el fichero:
themes/[current_theme]/page.tpl.php
En Drupal 7 he tenido que hacerlo en:
modules/system/html.tpl.php
Debemos añadir las siguientes líneas de código justo antes de la etiqueta </head>
http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML
Si además quiero que use HTML-CSS por defecto para que quede con mejor presentación
type="text/x-mathjax-config">
MathJax.Hub.Config({
MMLorHTML: { prefer: { Firefox: "HTML" } }
});
type="text/javascript"
src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
Una vez hecho esto, si escribo:
Esto es una integral \( \int_\Omega f(x)dx \) y esto \( \displaystyle\int_\Omega f(x)dx \)
\[ \int \ln(x) \;dx = \int 1 \cdot \ln(x) \;dx \ = x \cdot \ln(x) - \int x \cdot \frac{1}{x} \;dx \ = x \cdot \ln(x) - x \]
$$f(x)=\dfrac{x+1}{x-1}$$
Obtengo:
Esto es una integral <span id="MathJax-Element-1-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="∫Ωf(x)dx»>∫Ωf(x)dx∫Ωf(x)dx y esto <span id="MathJax-Element-2-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="∫Ωf(x)dx»>∫Ωf(x)dx∫Ωf(x)dx
<span id="MathJax-Element-3-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="∫ln(x)dx=∫1⋅ln(x)dx =x⋅ln(x)−∫x⋅1xdx =x⋅ln(x)−x»>∫ln(x)dx=∫1⋅ln(x)dx =x⋅ln(x)−∫x⋅1xdx =x⋅ln(x)−x∫ln(x)dx=∫1⋅ln(x)dx =x⋅ln(x)−∫x⋅1xdx =x⋅ln(x)−x
<span id="MathJax-Element-4-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="f(x)=x+1x−1″>f(x)=x+1x−1f(x)=x+1x−1
$$ \begin{align*}
2x^2 + 3(x-1)(x-2) & = 2x^2 + 3(x^2-3x+2)\\
&= 2x^2 + 3x^2 - 9x + 6\\
&= 5x^2 - 9x + 6
\end{align*} $$
<span id="MathJax-Element-5-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="2×2+3(x−1)(x−2)=2×2+3(x2−3x+2)=2×2+3×2−9x+6=5×2−9x+6″>2x2+3(x−1)(x−2)=2x2+3(x2−3x+2)=2x2+3x2−9x+6=5x2−9x+62×2+3(x−1)(x−2)=2×2+3(x2−3x+2)=2×2+3×2−9x+6=5×2−9x+6
$$
\frac{1}{\displaystyle 1+
\frac{1}{\displaystyle 2+
\frac{1}{\displaystyle 3+x}}} +
\frac{1}{1+\frac{1}{2+\frac{1}{3+x}}}
$$
<span id="MathJax-Element-6-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="11+12+13+x+11+12+13+x»>11+12+13+x+11+12+13+x11+12+13+x+11+12+13+x
$$
F(x,y)=0 ~~\mbox{and}~~
\left| \begin{array}{ccc}
F''_{xx} & F''_{xy} & F'_x \\
F''_{yx} & F''_{yy} & F'_y \\
F'_x & F'_y & 0
\end{array}\right| = 0
$$
<span id="MathJax-Element-7-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="F(x,y)=0 and |Fxx″Fxy″Fx′Fyx″Fyy″Fy′Fx′Fy′0|=0″>F(x,y)=0 and ∣∣∣∣∣F′′xxF′′yxF′xF′′xyF′′yyF′yF′xF′y0∣∣∣∣∣=0F(x,y)=0 and |Fxx″Fxy″Fx′Fyx″Fyy″Fy′Fx′Fy′0|=0
$$
|x| = \left\{ \begin{array}{rl}
-x &\mbox{ if $x<0$} \\
x &\mbox{ otherwise}
\end{array} \right.
$$
<span id="MathJax-Element-8-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: center; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="|x|={−x if x<0x otherwise»>|x|={−xx if x<0 otherwise|x|={−x if x<0x otherwise
Tercer Método
Con DruTeX
Es un módulo disponible para la versión 6 de Drupal. Necesita que el servidor tenga instalado <span id="MathJax-Element-9-Frame" class="MathJax" style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 14px; vertical-align: baseline; background: transparent; display: inline; font-style: normal; font-weight: normal; line-height: normal; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="LATEX»>LATEXLATEX.