Outlook 2016, 2013 and 2010 have a feature that helps users to quickly take screenshot of the open windows or screen clipping of those windows. And for taking the screenshot, you do not have to install any third party tool.
Launch New Message window in Outlook 2010 then navigate to Insert menu.
Navigate to Illustrations section and click the down arrow available next to Screenshot option.
This would provide the option to the user to include screenshot of the available windows. And if you want to include only part of the window then click the Screen Clipping from the menu list and select the required part that needs to be sent as Screenshot.
Note :- If you have got too many windows opened then make sure to minimize all the windows except the window from which the screen clipping has to be taken.