While it is technically *possible* that there's some sort of tracking going on, in the vast majority of cases there isn't.
Today's anti-virus programs watch for stuff like this. Because, if an email fires up a program that can track where an email has gone and report back to a marketer, then some other email could launch a program that installs itself on your computer to do all kinds of nasty things. Like, pop-up ads, keyboard watchers, or using your computer to send out spam, etc. So, if your anti-virus is up-to-date then you're pretty safe against this sort of tracking.
As for cookies or beacon images, those won't harm your computer. But they can be used for marketing statistics. Again, while it's technically feasible that reading an email with a web bug in it could be tied to the particular email address of the first person to get the email, that's not how they're usually used. And, anyone that person forwards it to will not have their email address tracked nor harvested by this method.
Mostly, the pleas to forward to other people are just someone wanting to spread their ideas as far as possible. Or, someone just playing a prank and trying to get people to forward nonsense all over the world.
99% of the "Please forward this to everyone" emails I get contain at least some misinformation, and often the entire email is completely flawed or a hoax. Even the ones that are trying to warn you of some great peril are usually worthless or outright dangerous, like HIV infected needles in coin return slots, gang member initiation rituals, kidnap attempts in parking lots, or simple procedures that will save someone in an emergency medical situation.
The website Snopes is not perfect, but the vast majority of forwarded emails are addressed on there. Use the search box to look for unique information in the email (names, places, etc.) and you'll find the email you just received. Most will turn out to be false.
Several years ago, when I would receive one of these emails from a friend or family member I would look it up on Snopes and then reply back to the person with the link to the Snopes article. It didn't take long before I stopped receiving these from most people. Either they started looking it up themselves (I hope.) Or, they just stopped including me in their forward lists.
There is one significant problem with *other* people forwarding these things. When someone sends one of these messages to you and 20 other people, your email address is now on the machines of 20 people. If 5 of them forward to 20 more people then your email address is now on about 100 different computers. (Because, by default, most email programs include the entire list of people the original was sent to when it creates the forwarded copy.) Repeat that a few times and pretty soon, without you doing anything, your email address is on thousands of computers.
Eventually, your email address will get forwarded to someone whose computer is infected with a virus. That virus scours the hard disk of the machine its on looking for email addresses to send spam to. That is where a lot of spam comes from.
That's also why you cannot trust the return address of emails sent to you. A lot of spam programs pull random addresses from nearby each other in a file. One will be put in the To: field and the other in the From: field. The idea being that if the addresses are close to each other in a forwarded email then maybe those two people know each other. That makes it more likely that someone will trustingly open an attachment in an email they think came from a techie friend.
Always heed the advice: Never open an email attachment that you were not expecting. If an email comes through with an attachment, always check with the sender before opening, even if it's someone you trust. You cannot be certain it came from their computer unless they verify that it did.