iOS 通过二进制判断图片类型

+ (NSString *)typeForImageData:(NSData *)data {

    uint8_t c;

    [data getBytes:&c length:1];

    switch (c) {

    case 0xFF:

        return @"image/jpeg";

    case 0x89:

        return @"image/png";

    case 0x47:

        return @"image/gif";

    case 0x49:

    case 0x4D:

        return @"image/tiff";

    }

    return nil;

}