1. //创建一个UIImage对象
2.     UIImage *image = [UIImage imageNamed:@"scene1.jpg"];
3. //1.建立bitmap Context
4.     UIGraphicsBeginImageContext(image.size);
5. //2.把原图绘制到context上
6.     [image drawInRect:CGRectMake(0, 0, image.size.width, image.size.height)];
7. //3.把水印文字绘制到context上。
8. //在左下角加水印
9.     CGRect textFrame = CGRectMake(0, image.size.height-40, 200, 40);
10. //设置水印文字属性
11.     UIFont *font = [UIFont boldSystemFontOfSize:30];
12.     NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
13.     style.alignment = NSTextAlignmentCenter;
14.     
15.     UIColor *color = [UIColor colorWithRed:254.0/255 green:201.0/255 blue:21.0/255 alpha:1];
16.     
17.     [text drawInRect:textFrame withAttributes:
18.      @{NSFontAttributeName:font,
19.        NSForegroundColorAttributeName:color,
20.        NSParagraphStyleAttributeName:style}];
21. //4.从bitmap context上获取加了水印以后的图片。
22.     UIImage *waterImage = UIGraphicsGetImageFromCurrentImageContext();
23. //5.关闭bitmap context。
24.     UIGraphicsEndImageContext();
25. //6.返回获取的图片
26.     return waterImage;
27.  
28.  
29. 此方法最好独立成一个单独的类，只需一类方法就能完成。