Nick La has made another great great tutorial for us. Nick La shows us how to decorate our images and photo galleries without editing the source images. The trick is very simple. All you need is an extra tag and apply a background image to create the overlaying effect. It is very easy and flexible with over 20 styles, from a simple image icon to a rounded corner to a masked layer (both decorative and complex). To change the look and feel, simply edit the CSS specifications of the span element. To show how flexible it is, Nick La has created 15 different styles as examples for us (notice the HTML markup is same).
Source: CSS Decorative Gallery