Back behind the Monsters, Inc. attraction in DCA is a private meet and greet for Disney Visa cardmembers. You must show your Disney Visa to get in, and then you will be able to meet the characters in this area. I've heard that it's either Chip & Dale, Goofy, or Pluto.
The CM will hand you a coupon for one free 5x7 photograph from PhotoPass during the meet and greet. In other words, if you met with Chip & Dale than your free photo is supposed to be with Chip and Dale, not Mickey at his house or a princess at the Fantasy Faire. However, many guests, myself included have been able to use the coupon for one free photopass picture, not necessarily from the Disney Visa meet and greet. You also have to get it done in the parks. Online will not work for this coupon.
Please note though that since the official policy is one photo from the Disney Visa Meet and Greet only, you may have a CM tell you that can't use it on a photo that did not come from the Visa Meet and Greet. When I did it, the CM told me that she didn't mind where the photo was from, but some people might so she wanted to give me a heads up on that.
If the CM does tell you it has be from the meet and greet, they are not giving you wrong information because the coupon says that it's only good for the Visa meet and greet. If this happens, your best option is probably to return later in the hopes of getting a different CM. Whatever happens, I advise people not to raise a fuss about it because this is a free perk that could be taken away if it becomes too much trouble. And it's not like the Visa meet and greet will feature non-popular characters.