"Nintendo" SVG files
See Only Resize-Friendly Scalable Vector Graphics (SVG) In Google Images | Lifehacker Australia
So what is so good about SVG? From the wiki page:
Scalable Vector Graphics (SVG) is a family of specifications of an XML-based file format for describing two-dimensional vector graphics, both static and dynamic (i.e. interactive or animated).
The SVG specification is an open standard that has been under development by the World Wide Web Consortium (W3C) since 1999.
SVG images and their behaviors are defined in XML text files. This means that they can be searched, indexed, scripted and, if required, compressed. Since they are XML files, SVG images can be created and edited with any text editor, but drawing programs are also available that support SVG file formats.