How can I detect an object (with the camera) within an image, and make a new image of this object?

Within my project I'm using the camera function of the iPhone. I'd like to take a picture of a card (Rect开发者_JS百科angle shape). After I take this picture I'd like to scale and fit this card to a new image.

Can anyone point me in the right direction for making these functions? (are there any libraries or so?)

Help is greatly appreciated

Read about OpenCV. It's easy to port it on iPhone. But it isn't so easy to use it. Grab a book about OpenCV for weekend reading and on monday you'll easy solve your task.