HTML5, CSS3, JS - Simple Background Slideshow.
Note 1: See page source.
Note 2: Have a look at the page in all browsers.
Note 3: Try resizing the window to see the effect.
Note 5: All pictures demod have different sizes and are automatically resized and can be dynamically rescalled.
Note 6: You can change transparency - see RGBA background-color style in the "div#myContainer".