简单的通过NSFileManager 存储图片

UIImage *image = [UIImage imageNamed:@"Default.png"];
    NSData *data = UIImageJPEGRepresentation(image,0.7);
    NSArray  *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = [paths objectAtIndex:];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *fullPath = [documentDirectory stringByAppendingFormat:@"/de.png"];
    [fileManager createFileAtPath:fullPath contents:data attributes:nil];