gabi,
unfortunately, the picture control cannot be rotated, so far as I have ever seen. You will probably need to do this within the picture control itself. I would suggest just enlarging the control and centering the image. Fill in the rest of the image with black so that you don't have to worry about the background (or use white and figure out how to backfill with white.)
I know it sounds difficult, but it is your only choice. Even the opsys to do this would perform the same operation. Its just not done for you yet.
Perhaps someone out there knows a shortcut. If so, it will save you some time, and I will learn something as well.
Good luck