The file extension certainly is a possibility, but the most common cause here is that the path to the image is not correct, so my money is on Karin Sue's suggestion:
You can put the image anywhere you like, but the above comment was made because, currently, you are telling the browser to find the image in the same folder as the web page itself.
Originally Posted by Karin Sue
However, if you had the image in a folder called /images/ that is in the same folder as basic.html, then the path should look like this:
<p><img src="logo_21460_web.jpeg" width="200" height="162"
There are many variations on that, so you have to consider the path (or link, or URL, or whatever you want to call it) very carefully. It's the same as giving someone directions to a location. You are telling the browser where to go to find the image. If your directions are wrong, it will get lost!
<p><img src="images/logo_21460_web.jpeg" width="200" height="162"