Projection of a formerly rendered image or animation onto a card, I'd say. With a warped simple shape as projection area and opacity mask.
But it would be perfect if this could be done in one session, but I wouldn't know how to achieve that.
EDIT: ah, it's a Nuke composite, didn't read that part. It can be done in one go in TG, but I came across an issue where the image was projected the wrong way, though the projection camera was the same as the inital render was made from.
Sorry about hijacking your thread, Richard. I will stop after this.