图片加水印效果的实现并保存至相冊
实现效果如图：
效果图

project下载：githubproject下载链接

代码：

- (void)viewDidLoad {
    [super viewDidLoad];

    UIImage *image = [UIImage imageNamed:@"pushu.jpg"];
    UIImage *waterImage = [self waterMarkImage:image withText:@"朴树水印測试"];

    UIImageWriteToSavedPhotosAlbum(waterImage, nil, nil, nil);  //保存图片至相冊

//    展示图片
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];
    imageView.image = waterImage;
    [self.view addSubview:imageView];

    // Do any additional setup after loading the view, typically from a nib.
}
- (UIImage *)waterMarkImage:(UIImage *)image withText:(NSString *)text {
    UIGraphicsBeginImageContext(image.size);

//    在画布中绘制内容
    [image drawInRect:CGRectMake(0, 0, image.size.width, image.size.height)];

//    绘制文字
    [[UIColor darkGrayColor] set];
    CGRect rect = CGRectMake(70, 220, 200, 60);
    NSDictionary *dic = @{NSFontAttributeName:[UIFont systemFontOfSize:30],
                          NSObliquenessAttributeName:@1};       //这里设置了字体，和倾斜度。具体其它參数文章结尾有具体说明的文章链接
    [text drawInRect:rect withAttributes:dic];

    //在iOS7之前用下列方法比較方便
//    [text drawInRect:rect withFont:[UIFont systemFontOfSize:30] lineBreakMode:NSLineBreakByWordWrapping alignment:NSTextAlignmentCenter];

//    从画布中得到image
    UIImage *returnImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return returnImage;
}
- (void)drawInRect:(CGRect)rect withAttributes:(NSDictionary *)attrs NS_AVAILABLE_IOS(7_0);

关于此方法，在iOS7以后应用。attrs设置參数的具体说明在例如以下链接文章中：
说明文章链接：attrs參数说明文章