Take screenshot from your android phone by adb
android-scrot will save a screenshot of your phone to the current directory
$ android-scrot
android_12-02-2014_11-17-43.png saved
$ android-scrot your-app
your-app_12-02-2014_11-18-04.png saved
$ android-scrot your-app.png
your-app.png saved
To get the screenshots from your phone you need to install adb from the android sdk. In Ubuntu you'll get that command by the android-tools-adb package, other distributions should ship similar packages. Optional is imagemagick to rotate the screenshot according to the orientation of the phone