There is a site that claims it can add or remove objects or people from a photo. They have a sample at http://www.pixsharp.com/en-us/dept_50.html where they removed several people from a group photo.

 

I've removed some objects from photos myself, but I do not see how this sample can be real. Look at the top left of the "before" photo, and you will see that a man is completely blocking the arm of the person standing beside him. In the "after" photo, the person's arm is fully visible. How is this possible if the arm wasn't in the original picture?

 

I don't see how they could have made the "after" photo from the "before" photo. It appears that they might have originally had the "after" photo, and added the other people to make the "before". However, then there is the problem with the extra arm on the right side of the photo. What do you think?

I'd put it down to lots of time, and low res image, but I didn't look at it for that long, the right hand side background is wrong if you look at the first pic...

Yes, that is another thing that made me think the sample could be fake. I suppose they could edit the background, but why would they do that if this is really a sample of their "remove people" service?

Well the background in the edited version is hidden in the unedited one...

Haha, I’d love to send them a picture with a complicated background, like a fractal or something.

I suspect the "filling in background that wasn't there before" bit is why they are proud of the service.

 

And in answer to the how question, it is either a complex sampling and extrapolation algorithm, or it's done by hand (much more likely imho).

I've done stuff like that before. It's very time consuming though. As for the arm of the man on the left in glasses. I would have cloned his sleeve, then for his arm I would have cloned an area of his neck then re-scalled it. This should provide a properly illuminated arm. If that proved too difficult I'd use part of the arm from the man on the right for cloning.

 

Everything else, moving people, removing people and adjusting the background is quite straight forward.