Keeping your website’s content updated and fresh is not an easy job to do, it costs both time and money.
If this happens, the browser will display a corrupt image, or nothing at all.
Your clients will end up having to download more and the web server will be sending data it doesn't have to.
A more elegant approach is shown in the AJAX example.
Image updating is useful if you have dynamic graphs or perhaps a webcam. The main trick is appending a date string after the image file name to make sure the browser does not use a cached version of the image.