OpenCV2.0 has several computer vision and image processing tools. Specifically warpAffine (by defining the rotation matrix) will solve your problem with rotating an image.

The 2x3 transformation matrix mentioned in the documentation is as follows:

where θ is the angle of rotation and t_x and t_y is the translation along the x and y axes respectively.

You can get the source code here.

Also, OpenCV2.0 has many MATLAB-esque functions like imread, etc.