微时间不准确的时间测量？

I just found out about microtime() in PHP. I tried to check how long it will take to execute basic image load. Here is code:

<?php
$start = microtime(true);


    echo("<img src='http://example.com/public/images/new.png'/>");

    $time_elapsed_secs = microtime(true) - $start;
    echo($time_elapsed_secs);
?>

On average it returns: "8.8214874267578E-6" which I assume means 8.82 seconds? Did I do something wrong? I am sure image loads faster than 8 seconds, I would definitely notice 8 seconds.

Here is image itself:

The E-6 at the end of that string means you need to move the decimal six places to the left.

By the way, the echo statement executes almost instantly, writing that HTML to the output stream. That doesn't mean the image loaded that fast in some remote browser reading the HTML stream and trying to load the image.