With time you may get bored to the user display picture of yours which is shown at the login screen and in windows start menu. In such case you might want to change the user display avatar picture which is allowed in windows but you cannot take a screenshot of something and then add it as user display picture.
User Picture Enhanced is a freeware program which allows you to add and remove the default user display pictures. It adds pictures by using a screen-shot tool that can be re-sized. There is also an option to import some pre-shot images.
However you cannot add a picture other than a bitmap image format with this tool, and a beyond a specific size which you can always do with default windows interface, but it can set a user display picture using a screenshot.
In all, I would recommend to use both the technique to change the user display picture in windows including the windows default way and using this software as per your requirement.
Note: If you are wondering how could you add animated display pictures in windows, then you cant add one as per my research if still there is a way please do share it with us through comments.