If the picture is not on the Web, upload it to your Web server or any photo-hosting site. Open the HTML file for the Web page that you want to enhance with a picture in your text editor.

How to Add an Image to a CSS File. Web pages normally add images using the inline HTML "img" tag. CSS coding usually doesn't set an image's source because CSS controls design rather than content.

Now if this was the HTML page itself, it would be pretty easy to send an HTTP header to clue in the browser (force expiry IIRC), but the browser will ask for the image in a separate connection ...