What app/feature/software is this microphone image from? What is this microphone image from? It appeared on my friend's MacBook and she can't figure it out.
This is the Mac OS X built in voice input mechanism.



To turn it off, visit preferences - it's possible to turn it on via a keyboard shortcut which may explain it's random appearance.




  Speech Recognition
  
  Speakable Items, built into OS X and located in the Speech pane of
  System Preferences, lets you control the computer using your voice
  instead of the keyboard. And you don’t have to train your Mac to use
  it. You can use Speakable Items to navigate menus and enter keyboard
  shortcuts; speak checkbox names, radio button names, list items, and
  button names; and open, close, control, and switch among applications


This article from Lifehacker explains how to use the feature is you are interested in learning more.