The result is that each hit of the HTML page can cause one of many possible images to be used. Email aliases are not the same thing as email boxes. Email boxes live on email servers and are used to store your email until you download it. Email boxes are analogous to post office boxes in the physical world. That is, your email is stored on the email server until you retrieve it.
Email forwarding is analogous to post office mail forwarding in the physical world.
That is, email arrives addressed for one recipient and is forwarded to another location. As an example, you might have an email box at an Internet Service Provider or at an online service. Your real email box must be able to accept email through the Internet. This allows you to give your customers one set of email addresses, but leaves you the liberty to change the person who should get that email. Each alias you choose must be unique regardless of the domain name.