How to make an image of a piece of a score
MuseScore 1.x lets you save files in many formats including graphics and audio, but doesn't have a built-in way to select only a portion of the file. This workaround uses a separate file for exporting and works great.
As of MuseScore 2.x, there will be a feature to make it even easier to create snippets of your sheet music: http://musescore.org/en/foto-mode