UIImage *myImage = loadUnwatermarkedImage();
NSString *myWatermarkText = @"Watermark";
UIImage *watermarkedImage = nil;

UIGraphicsBeginImageContext(myImage.size);
[myImage drawAtPoint: CGPointZero];
[myWatermarkText drawAtPoint: CGPointMake(10, 10) withFont: [UIFont systemFontOfSize: 12]];
watermarkedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

完成后， watermarkedImage 将是一个自动释放的水印图像。 loadUnwatermarkedImage（）是一个提供原始图像的虚构函数。

Upon completion the watermarkedImage will be an autoreleased watermarked image. loadUnwatermarkedImage() is a fictional function providing an original image.