Rotate an image by 90 degrees
Assuming that you will want to do more interesting things with these images later, you should probably come up with a better OOP design.  I suggest:

public interface ImageTransformation {
    public Pixel[][] transform(Pixel[][] image);
}

public class Clockwise90Rotation implements ImageTransformation {
    ...
}

public class AntiClockwise90Rotation implements ImageTransformation {
    ...
}


It's practically no work to rearrange the code that way.  In return, you gain the flexibility to do things like:

ImageTransformation[] pipeline = new ImageTransformation[] {
    new Clockwise90Rotation(),
    new ContrastEnhancer(),
    new GaussianBlur(/* radius= */ 5)
};
for (ImageTransformation t : pipeline) {
    image = t.transform(image);
}