We made this really fancy demo for our promotional website of our new Photoshop plugin we made in cooperation with Subtle Patterns.
It works only on Webkit-based browsers because of
-webkit-mask-image
which I used make that fading transition.
You can look into source code to find out more. Hint: there are two identical elements stacked on each other and the top one is masked when we need to show the bottom one.
See the website in action