It is a repeated problem with Linux, it is How to take screenshots in Linux. There many ways to accomplish it and here it a list of them for reference.
scrot (SCReen shOT) is a simple commandline screen capture utility that uses imlib2 to grab and save images. Multiple image formats are supported through imlib2’s dynamic saver modules.
#apt-get install scrot
scrot '%Y-%m-%d_$wx$h.png' -e 'mv $f ~/shots/' # This would create a file called something # like 2000-10-30_2560x1024.png and move it to your shots directory.
Shutter is a feature-rich screenshot program. You can take a screenshot of a specific area, window, your whole screen, or even of a website – apply different effects to it, draw on it to highlight points, and then upload to an image hosting site, all within one window.
#apt-get install shutter
The import program is a member of the ImageMagick(1) suite of tools. It saves any visible window on an X server and outputs it as an image file. You can capture a single window, the entire screen, or any rectangular portion of the screen.
#apt-get install imagemagick
$ import screenshot.png # Will show a + shaped pointer which upon clicking a window will save it
Screenshot application for GNOME.This tool takes a picture of the desktop or of a window and saves it
into a file.
#apt-get install gnome-screenshot
Xwd is an X Window System window dumping utility. Xwd allows X users to store window images in a specially formatted dump file.
#apt-get install x11-apps #apt-get install imagemagick
$ xwd -silent -root | convert - screenshot.png
#apt-get install fbcat
$ fbgrab my_screenshot
There are many other application to name a few kazam, kgrab, nanoshot etc