Unlike with the jpg image format, transparent gifs (image files with a suffix of .gif) provide an empty background to your image, allowing the background to become whatever is behind the .gif on the web page.

The image on the top left here shows what the original transparent .gif file looks like in Photoshop. The other three images show what that same .gif file will look like against different backgrounds.

Photographs can be edited to remove the background, allowing the main image in the photograph to blend in with the rest of the page, rather than framing it as a separate picture. The result can add substantial visual power to your web pages, giving them a strong, clean professional look without a lot of expense — an especially efficient way to spice up your web site.

The effect is strongest when the colors in the background are relatively uniform — the results may not be as strong if the background contains many different colors.

To learn more about Gifs, see Wikipedia’s entry describing them.