An example HTTP response.

HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 57

<html>
<img src="http://example.org/image.png" />
</html>
Because of the img tag, the browser makes a second request.

GET /image.png HTTP/1.1
Host: example.org
User-Agent: Mozilla/5.0 Gecko
Accept: text/xml, image/png, image/gif, */*