给图片添加文字水印

- (UIImage *) addTextToImage:(UIImage *) baseImage text:(NSString *)text  atRect:(CGRect) rect{
    int w = baseImage.size.width;
    int h = baseImage.size.height;
    UIGraphicsBeginImageContext(baseImage.size);
    [[UIColor redColor] set];
    [baseImage drawInRect:CGRectMake(0, 0, w, h)];
    [text drawInRect:rect withFont:[UIFont systemFontOfSize:20]];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}