裁剪和打水印

  UIImage *oldImg = [UIImage imageNamed:@"haha"];
    CGFloat gap = 2;//圆环的宽度
    CGFloat ctxW = oldImg.size.width  + 2 * gap;
    CGFloat ctxH = oldImg.size.height + 2 * gap;
    CGSize imgSize = CGSizeMake(ctxW, ctxH);//
    UIGraphicsBeginImageContextWithOptions(imgSize, NO, 0.0);
    CGContextRef ctx =  UIGraphicsGetCurrentContext();
    //    画大圆
    [[UIColor blueColor] set];
    CGFloat bigRadius = ctxW * 0.5;
    CGFloat cententX = bigRadius;// 圆心
    CGFloat cententY = bigRadius;// 圆心
    CGContextAddArc(ctx, cententX, cententY, bigRadius, 0, M_PI * 2, 0);
    CGContextFillPath(ctx);//画圆
    //     画小圆 跟大圆是同心圆
    CGFloat smallRadius = bigRadius - gap;
    CGContextAddArc(ctx, cententX, cententY, smallRadius, 0, M_PI * 2, 0);
    //裁剪
    CGContextClip(ctx);
    //绘图

    [oldImg drawInRect:CGRectMake(gap, gap, oldImg.size.width, oldImg.size.height)];
    UIImage *newImg  =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    UIImageView *imgs = [[UIImageView alloc]initWithImage:newImg];
    [self.view addSubview:imgs];
    NSData *data = UIImagePNGRepresentation(newImg);
    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)lastObject] stringByAppendingPathComponent:@"exit.png"];
    [data writeToFile:path atomically:YES];
    NSLog(@"%@",path);

打水印

        UIImage *bgImg = [UIImage imageNamed:@"seas"];
    // 创建一个基于位图的上下文 UIGraphicsBeginImageContextWithOptions （图片大小，透明度（NO透明），缩放比例(0.0默认比例)）
        UIGraphicsBeginImageContextWithOptions(bgImg.size, NO, 0.0);
        // 画背景 将背景图画在bitmap上下文中
        [bgImg drawInRect:CGRectMake(0, 0, bgImg.size.width, bgImg.size.height)];
        // 画右下角图片logo水印
       UIImage *waterMark = [UIImage imageNamed:@"sina"];
        CGFloat scale = 0.2;//缩放比例
        CGFloat margin = 5;// 间距
        CGFloat waterMarkW = waterMark.size.width * scale;
        CGFloat waterMarkH = waterMark.size.height * scale;
        CGFloat waterMarkX = bgImg.size.width - waterMarkW - margin;
        CGFloat waterMarkY = bgImg.size.height - waterMarkH - margin;
        [waterMark drawInRect:CGRectMake(waterMarkX, waterMarkY, waterMarkW, waterMarkH)];
        // 画右下角昵称水印
        NSString *names = @"@weibo.com/yourID";
        NSMutableDictionary   *arrs = [NSMutableDictionary dictionary];
        arrs[NSForegroundColorAttributeName] = [UIColor whiteColor];
        [names drawInRect:CGRectMake(waterMarkX - 100, waterMarkY + margin,150,50) withAttributes:arrs];
        //  生成新的合成图片
        UIImage *newImage =  UIGraphicsGetImageFromCurrentImageContext();
        //结束上下文释放内存
        UIGraphicsEndImageContext();
    // 显示到uiimageview中
    self.imageViews.image = newImage;
    //保存图片 将UIImage对象压缩成二进制数据 png图片质量最高
    NSData *data = UIImagePNGRepresentation(newImage);
    // NSDocumentDirectory写入沙盒的document文件夹 NSUserDirectory代表当前用户环境下搜索 expandTilde是否展开波浪线~该值为YES即表示写成全写形式，为NO就表示直接写成“~”
    NSString *path =  [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"大海啊蓝.png"];
    NSLog(@"%@",path);
    // 写入指定文件目录 真机环境一般写入沙盒
    [data writeToFile:path atomically:YES];
    //上传服务器

可以将img抽调成一个分类文件 用于快速开发