保存图片信息通过NSData保存到本地文件中

//第一步：保存头像信息到NSData中

   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);  
   self.documentsPath = [paths objectAtIndex:0];  

   NSString *imagePath = [NSString stringWithFormat:@"%@/%@.jpg", self.documentsPath, contacts.Photo]; 
   UIImage *tempImage = [UIImage imageWithContentsOfFile:imagePath]; 
   headOldImageData = [NSData dataWithData:UIImageJPEGRepresentation(tempImage, 1.0)]; 
   [headOldImageData retain]; 

//第二步：修改后用writeToFile归档

    NSString *imagePath = [NSString stringWithFormat:@"%@/%@.jpg", self.documentsPath, oldImageName];  
    
 
    if([fileManager fileExistsAtPath:imagePath])  
    {  
        [headOldImageData writeToFile:[NSString stringWithFormat:@"%@/%@.jpg", self.documentsPath, oldImageName] atomically:YES];  
    }