Jeff Croft have written an excellent article on using transparent PNG in web design, especially that it is now supported with IE7. The advantages of using transparency with PNG is the great image compression format, the color depths and the alpha-channel transparency; an advantage of PNG againt GIF which offer a limited binary transparency. Jeff shared in the article some great techniques that you can use with the general layout, logo, icons and content.
What if I wanted to place my personal logo on all of my photographs? Yes, it’s possible to open each image in Photoshop, apply the logo, and resave the image. However, this becomes terribly impractical when dealing with thousands of images that are frequently updated-and sometimes updated when I’m nowhere near a computer (for example, when I send photos to Flickr via my cell phone). Wouldn’t it be nice if the logo were added automatically? PNG can help do just that.