Yeah, this is another instance of a valid coupon being scanned and then posted to the web as a scam. As Inertia said, the coupons in the above link are invalid since they have been reproduced (and also altered).
The original coupon was a printable coupon that someone "won" in the following promotion:
To participate in this promotion validly, you have to register, give them your name, address and email, and then play the game by entering UPC codes for m&m's products. If you win they will email to you a link that allows you to print one coupon, directly to your printer only, via an Active-X control. Of course, you don't win every time you enter.
If you wish to participate in the official contest, here are some UPC codes to help you along (you can enter one instance of each UPC per email address per week):
If you win, the printed coupon will have your name displayed on it. It will also have some sort of identifying/audit information in the rectangular dot-scan graph in the upper right corner. I don't know if whoever posted the scanned images altered the dot-scan graph or not.
As to whether or not you will be able to use the scanned coupons that were posted, I can't say. They are reasonable facsimiles, and even the official coupons have to printed on your home printer, but the scanned coupons aren't legally valid. I'll leave questions of moral validity to each individual. In any event, they weren't meant to be duplicated and used to obtain a windfall of free m&m's.