The com.jme3.app.state.ScreenshotAppState enables your users to take screenshots of the running game.
You activate this feature as follows in your simpleInitApp() method:
ScreenshotAppState screenShotState = new ScreenshotAppState(); this.stateManager.attach(screenShotState);
The default screenshot key is KeyInput.KEY_SYSRQ, alos known as "System Request / Print Screen" key. On Mac keyboards, this key does not exist, so on Mac OS you take screenshots using Command+Shift+3 (fullscreen) or Command+Shift+4 (windowed: press space to select a window and then click).
The screenshot is saved to the user directory.