If you need to have an tag be dynamic (in this case, I wanted to reference my weather station graphs from Weather Underground and ensure I had "today's" graph without updating the HTML by hand), then this is the way to do it. I made it more verbose just for illustration, but you can reduce the code-size dramatically if that's important to you.

The "trick" is to just use an <img> tag with a unique id and then add some javascript right after it (or via one of your favorite libraries such as jQuery) that used the DOM-maniuplation javascript functionality to change the src attribute to the text of where you want it to come from. In this case, I have it dynamically updating the year, month and day in the URL for the Weather Underground images.