When an Android device is connected via USB to the computer, you can take a screenshot via adb:
$ adb shell screencap -p | perl -pe 's/\x0D\x0A/\x0A/g' > file.png
On a Tolino e-book reader, this unfortunately added some textual information before the actual PNG image data:
vinfo.xoffset = 0 vinfo.yoffset = 2144 vinfo.xres = 1448 vinfo.yres = 1072 vinfo.xres_virtual = 1472 vinfo.yres_virtual = 3456 .PNG...
The solution is to use grep in binary mode to remove those:
~/bin/android-screenshot
#!/bin/sh adb\ shell screencap -p\ | grep -a -v '^vinfo\.' \ | perl -pe 's/\x0D\x0A/\x0A/g' \ > "screenshot-`date --rfc-3339=seconds`.png"