Comment 2 for bug 1284790

via Google+, there's apparently a new way to do this now. I guess the script should be re-written as a wrapper for this.

Ricardo Salveti originally shared:

Ubuntu Touch image 230 also brings a new way to take screenshots, and this time grabbing the texture from Mir directly (and making it compatible with any other device that is also using Mir by default).

How to easily get a screenshot with Mir:
$ adb shell mirscreencast -m /tmp/mir_socket -n1
Starting screencast for output id 1
$ adb pull /tmp/mir_screencast_768x1280.rgba
4788 KB/s (3932160 bytes in 0.801s)
$ convert -size 768x1280 -depth 8 mir_screencast_768x1280.rgba screenshot.png

You could also use mirscreencast to do a proper screencast (and not just one frame), but be careful as that will dump a huge amount of data in your disk :-)