What's a CSS Sprite, you may ask. Well, you can see it in action below:
You can create such CSS sprites automatically, for free, by using http://css-sprit.es/. All you have to do is select a bunch of different images, the effect (it supports 6 different effects) - in my example I have used "Desaturate" - and that's it. You will instantly receive the image, the CSS and HTML code ready to be used into your website.