For this problem, i solve it by installing gnome-utils (Gnome Desktop Utilities) by Synaptic Manager or Software Manager,you can search for gnome-utils and install it. Tadaa…! It solved my problem..!
There is a new shortcut on : Menu-Accesories-Take Screenshot
you can take a screenshot now after that menu available.
you can see host key for screen shoot on : System Tool-System setting-Keyboard-Tab Shorcut (Linux Mint).
sorry about my bad english.