Bitmap bmp = new Bitmap(PbImame.Image);
bmp.RotateFlip(RotateFlipType.RotateNoneFlipX);
//Show them in a picturebox
PbImageMirrored.Image = bmp;
Or
Bitmap bmp = new Bitmap(PbImame.Image);
// public Mirror(bool mirrorX, bool mirrorY)
Accord.Imaging.Filters.Mirror filter = new Accord.Imaging.Filters.Mirror(false, true);
filter.ApplyInPlace(mirror);
PbImageMirrored.Image = bmp;