Would it be possible to explain further what you mean by changing the vertical/horizontal perspective? Do you mean to distort the image so that it becomes thinner on one or more sides, or something different? If you have a link to an example image that could really help.
I too would like this feature. For example, if you have a camera tilted up and take a picture of a cathedral, the vertical lines will converge. This can be post fixed in programs like Photoshop. They call it a filter for distortion. It allows straightening the vertical lines so they become more parallel.