How to rotate some part of image?

I have dataset of finger images; but some fingers are not captured in straight way; and they are misalighned at some other angle due to which I cannot get mask of that image properly. Now I want to rotate all those fingers only so that background can be removed easily with well alighned fingers. Following is misalighned finger image.

I need images with straight fingers.

How I can do it?

[Matt J]

How is the orientation of the finger measured?

How are you getting the mask when the finger is aligned the way you'd like it?

[Imran Riaz]

This is the masked image in above figure. I also want to remove the black area. But when i apply loop to select the only 1's values and ignore the zeros. The image is cut down from right side and from left side some black portion at bottom side is also present.

So if the fingure is in straight position it can be easily removed.