Inkscape is a free Open Source program similar to Adobe Illustrator. It is incredibly powerful and it is able to output **.SVG** graphics files. Why is this so good? Because you can scale the pictures as large or a small as you want without losing any picture definition. This is ideal for making images to wrap around 3D models.

Educational Examples

Article on using Inkscape in schools to teach Math, Technology, Art and Creativity

Tutorials from the above site in more detail:

More fun tutorials online

Using Inkscape to make text based portraits:

Making leaf textures for trees using inkscape tutorial:

Example of using Inkscape SVG textures in Blender:

Screencast of making a Vitamin bottle in Blender and a label to go on it in Inkscape :

How to bring Inkscape, Gimp and Blender together tutorial gif