Watch the Network tab. Two rows appear, in this order:
one-image.html — type document, the HTML itself.badge.png — type png, fetched only because the
browser found the <img> tag below while reading the
HTML.
The HTML file itself contains no picture data at all. It contains a
reference: <img src="images/badge.png">. That is an
instruction to go and fetch a second file. View the source of this page and you
will see the tag is a single short line, yet the browser makes a whole extra
request for it.