Check if sent email has been read

Recently while working upon a project, I was asked to implement the functionality to notify the user whenever the email sent is read.

What I did was, embedded an html image tag with the source set to a URL upon hitting which the email status would change to "Read" and a tiny invisible image would be returned in order to prevent it from showing the broken image i.e. something along the lines of following

<img src="http://foobar.com/email/read/{Record Id}" />;

How would have you gone about doing this? Do share it in the comments section below.