IPhone : How to detect current orientation to rotate UIImage?

I am implement taking photo function and I got an bellow issue.

After taking photo, I have to crop a thumbnail from original image to make avatar icon. But it's not good if user rotates the iPhone and take it. Step:

1. 
   

   Turn on camera.

   
   


2. 
   

   Rotate the iPhone to right ( it means landscape mode ).

   
   


3. Take picture.


4. I get UIImage with bad orientation. Therefore, thumbnail is not good.

How I can detect the orientation to rotate UIImage?

Thank you!