If you've worked with graphic softwares like Freehand, you should be familar with the Bezier Curve. 

According to WiKipedia, In the mathematical field of numerical analysis, a Bézier curve is a parametric curve important in computer graphics and related fields. Generalizations of Bézier curves to higher dimensions are called Bézier surfaces, of which the Bézier triangle is a special case.

I used GD graphic library and eval() fucntion is PHP to develop the Bezier class. This class takes the coordinates of 4 points needed for a bezier curve and draws it in an image. This image can be saved like any other web image. You can draw your own Curve by clicking on the following sample image.

The class code can be downloaded from my page in phpclasses.org.