how to calculate the angle of rotated image

If i have an image that is already rotated ... lets say just like the image attached ... how can i calculate the angle of the rotation and rotate the image again to return it to its normal "straight"

[madhan ravi]

upload your code

[Mahmoud Hassan]

bro , my code isn't concerned with what i wanna do now ... if u received this image from a scanner ... how can u rotate this image to make it straight ... and you don't know the angle of rotation

Answer 1

[KSSV]

I = imread('Empreinte3.bmp') ;
I1 = imrotate(I, 90) ;
imshow(I1) ;