问题描述：

    拍照完成后如果直接使用图片比如使用这个UIImage赋值给一个UIImageView的实例，显示出来的图片是完全没有问题的。但如果使用这个UIImage作他用，比如上传到服务器，就会出现问题了，上传到服务器的图片也是旋转了90度的。

问题原因：

    通过UIImagePickerControllerOriginalImage这个key从info字典中可以获取到拍照后的UIImage，它本身的imageOrientation属性是3，即是UIImageOrientationRight。如果对它进行裁剪、缩放等操作后，它的这个imageOrientation属性会变成0，造成照片内容和imageOrientaion不匹配。此时这张图片用在别的地方就会发生旋转。imageOrientation是只读的，不能直接修改其值。

解决办法

1.  设置相机的一个属性allowsEditing为YES，设了这个值，你拍完照片后会在照片上出现一个框框，这就是对照片的裁剪编辑。在相机的代理方法中取照片的时候就别用UIImagePickerControllerOriginalImage来取了，要用UIImagePickerControllerEditedImage。用这个key取出来的照片，它的imageOrientation是0，所以之后的任何裁剪、缩放操作都不会造成旋转。这是第一种方法。

2.  在对照片进行处理之前，先将照片旋转到正确的方向，并且返回的imageOrientaion为0, 方法如下:

-(UIImage *)fixOrientation:(UIImage *)aImage {
    // No-op if the orientation is already correct
    if (aImage.imageOrientation ==UIImageOrientationUp)
        return aImage;
    // We need to calculate the proper transformation to make the image upright.
    // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
    CGAffineTransform transform =CGAffineTransformIdentity;
    switch (aImage.imageOrientation) {
        case UIImageOrientationDown:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width,0);
            transform = CGAffineTransformRotate(transform, M_PI_2);
            break;
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);
            transform = CGAffineTransformRotate(transform, -M_PI_2);
            break;
        default:
            break;
    }
    switch (aImage.imageOrientation) {
        case UIImageOrientationUpMirrored:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width,0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.height,0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
        default:
            break;
    }
    // Now we draw the underlying CGImage into a new context, applying the transform
    // calculated above.
    CGContextRef ctx =CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,
                                            CGImageGetBitsPerComponent(aImage.CGImage),0,
                                            CGImageGetColorSpace(aImage.CGImage),
                                            CGImageGetBitmapInfo(aImage.CGImage));
    CGContextConcatCTM(ctx, transform);
    switch (aImage.imageOrientation) {
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            // Grr...
            CGContextDrawImage(ctx,CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);
            break;
        default:
            CGContextDrawImage(ctx,CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);
            break;
    }
    // And now we just create a new UIImage from the drawing context
    CGImageRef cgimg =CGBitmapContextCreateImage(ctx);
    UIImage *img = [UIImage imageWithCGImage:cgimg];
    
    CGContextRelease(ctx);
    CGImageRelease(cgimg);
    return img;
}