You have Windows or Linux guests running in VirtualBox with MacOSX as host and now you want to take some screenshot inside the guests? Well, there’s an easy way to do with MacOSX and you don’t need to install any kind of capture softwares in the Guests. Here’s how
1. By default, the Left Command is the Host key, if you’ve install the "Guest Addition" then the mouse & keyboard is automatically bound to the Guest when you move upon them, you can see the "green-down-arrow" indicates that mouse & keyboard is toggled on
So we need to turn it off by pressing Left Command key once, the "green-down-arrow" becomes "black-down-arrow"
2. Now you can use your shortcut key for taking screenshot from Mac
Press Right Command + Shift + 4 (read this post for more shortcut key to take screenshot in Mac), the pointer turns to a cross-point, now you can drag on the Guest OS to select the region that you want to take screenshot, here’s mine