問題描述：

    拍照完成后如果直接使用圖片比如使用這個UIImage賦值給一個UIImageView的實例，顯示出來的圖片是完全沒有問題的。但如果使用這個UIImage作他用，比如上傳到服務器，就會出現問題了，上傳到服務器的圖片也是旋轉了90度的。

問題原因：

    通過UIImagePickerControllerOriginalImage這個key從info字典中可以獲取到拍照后的UIImage，它本身的imageOrientation屬性是3，即是UIImageOrientationRight。如果對它進行裁剪、縮放等操作后，它的這個imageOrientation屬性會變成0，造成照片內容和imageOrientaion不匹配。此時這張圖片用在別的地方就會發生旋轉。imageOrientation是只讀的，不能直接修改其值。

解決辦法

1.  設置相機的一個屬性allowsEditing為YES，設了這個值，你拍完照片后會在照片上出現一個框框，這就是對照片的裁剪編輯。在相機的代理方法中取照片的時候就別用UIImagePickerControllerOriginalImage來取了，要用UIImagePickerControllerEditedImage。用這個key取出來的照片，它的imageOrientation是0，所以之后的任何裁剪、縮放操作都不會造成旋轉。這是第一種方法。

2.  在對照片進行處理之前，先將照片旋轉到正確的方向，并且返回的imageOrientaion為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;
}