This one is especially useful for the new bie because when you start with building webparts for SharePoint 2010, you often come to a point where you wanna add a URL somewhere, lets say programatically or in the CSS or may be in the ASCX code and you wonder, hey wait a minute where are the images for SharePoint placed anyway? How do I refer to them? So here’s your answer.
What you do is that you Right Click the Web parts project > Add > SharePoint “Images” Mapped Folder option. Doing that will give you an images folder inside your project directory and you can refer to that like this: