Simple pop-in window, darken the browser

Hi guys, I was wondering if you could help me out with a simple pop-in window - a window within the browser that will hold an image. Either script or a point in the right direction would be much appreciated thanks:

  • Click a button
  • Webpage is darkened
  • An image opens in a pop-in window
  • Clicking anywhere closes the pop-in window

Thanks in advance for your help!