PNG (short for Portable Network Graphics) images are a good choice for saving graphics to use in web pages. They have a ".png" extension (officially pronounced as ping).
PNG images are useful for web page graphics because they can contain full 8-bit transparency (unlike GIF images which only support 1-bit transparency) and they are well supported in almost all browsers.
Important: PNG images with transparency do not render properly in Internet Explorer (prior to version 7). To get around this, you can either use GIF images or use one of the workarounds to fix PNG rendering in Internet Explorer. If your images do not include transparency then they will work fine in Internet Explorer natively.