How to reshape an apple image from its real shape to a perfect circle?

I have several images of apples from different points of view. This means that the shape of the apples in the images, first of all is not the same.Of course, the shape is not a perfect circle as the apple is a natural product.

I would like in order to compare them, average, etc, to perform some kind of morphing to each apple image, so as to transform it to an image of a perfectly circular "apple" - with the new intensity values as close as possible to the real ones.

Any ideas or morphing code that could implement something like this? Thanks