（1）方式一

// static NSString *boundry = @"----------V2ymHFg03ehbqgZCaKO6jy";//设置边界
-(void)uploadDataWithURL:(NSString *)url postData:(NSDictionary*)postData image:(UIImage *)image {
    NSURL *reqUrl = [NSURL URLWithString:url];
    NSMutableURLRequest *urlRequest = [[NSMutableURLRequest alloc] initWithURL:reqUrl cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:30];
    urlRequest.HTTPMethod = @"POST";
    //设置请求头 在请求头中添加content-type字段
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; charset=utf-8;boundary=%@",boundry];
    [urlRequest setValue:contentType forHTTPHeaderField:@"Content-Type"];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    //NSURLSession
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:[[NSOperationQueue alloc]init]];
    //定义上传操作
    NSURLSessionUploadTask *uploadTask = [session uploadTaskWithRequest:urlRequest fromData:[self getBodydataWithImage:[UIImage imageNamed:@"chat_send_nor"]] completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        NSLog(@"响应结果:%@", response);
        NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"返回数据:\n%@",str);
    }];
    [uploadTask resume];
}

- (NSData *)getBodydataWithImage:(UIImage *)image{
    NSData *fileData = UIImageJPEGRepresentation(image, 0.8);
    NSString *fileName=@"image";
    NSMutableString *bodyString = [[NSMutableString alloc] init];
    [bodyString appendFormat:@"--%@\r\n",boundry];
    [bodyString appendFormat:@"Content-Disposition: form-data; name=\"FileName\"\r\n"];
    [bodyString appendFormat:@"Content-Type: text/plain; charset=\"utf-8\"\r\n\r\n"];
    [bodyString appendFormat:@"aaa%@.jpg\r\n",fileName];
    
    //PostID
//    [bodyString appendFormat:@"--%@\r\n",boundry];
//    [bodyString appendFormat:@"Content-Disposition: form-data; name=\"PostID\"\r\n"];
//    [bodyString appendFormat:@"Content-Type: text/plain; charset=\"utf-8\"\r\n\r\n"];
//    [bodyString appendFormat:@"%@\r\n",self.uuID];
    
    //pic
    [bodyString appendFormat:@"--%@\r\n",boundry];
    [bodyString appendFormat:@"Content-Disposition: form-data; name=\"file\"; filename=\"%@.jpg\"\r\n",fileName];
    [bodyString appendFormat:@"Content-Type: image/jpeg\r\n\r\n"];
    //[bodyString appendFormat:@"Content-Type: application/octet-stream\r\n\r\n"];
    
    //string --> data
    NSMutableData *bodyData = [NSMutableData data];
    //前面的bodyString, 其他参数
    [bodyData appendData:[bodyString dataUsingEncoding:NSUTF8StringEncoding]];
    //图片数据
    [bodyData appendData:fileData];
   
    //结束的分隔线
    NSString *endStr = [NSString stringWithFormat:@"\r\n--%@--\r\n",boundry];
    //拼接到bodyData最后面
    [bodyData appendData:[endStr dataUsingEncoding:NSUTF8StringEncoding]];
    return bodyData;
}

（2）方式二

-(void)uploadDataWithURL:(NSString *)url image:(UIImage *)image{
    NSData *data;
    UIImage *image1 = [UIImage imageNamed:@"chat_send_nor"];
    if ((data = UIImageJPEGRepresentation(image1, 1)) == nil){
        data = UIImagePNGRepresentation(image1);
    } else {
        //图片压缩方式1
        /*
         CGFloat compression = 0.9f;
         CGFloat maxCompression = 0.1f;
         data = UIImageJPEGRepresentation(image1, compression);
         while ([data length] > 1*100*1024 && compression > maxCompression) {
         compression -= 0.1;
         data = UIImageJPEGRepresentation(image1, compression);
         }
         */
        
        //图片压缩方式2
        NSInteger maxLength = 100 * 1024;
        CGFloat compression = 1;
        data = UIImageJPEGRepresentation(image1, compression);
        if (data.length > maxLength) {
            CGFloat max = 1;
            CGFloat min = 0;
            for (int i = 0; i < 6; ++i) {
                compression = (max + min) / 2;
                data = UIImageJPEGRepresentation(image1, compression);
                if (data.length < maxLength * 0.9) {
                    min = compression;
                } else if (data.length > maxLength) {
                    max = compression;
                } else {
                    break;
                }
            }
        }
    }
    NSString *boundary = [NSString stringWithFormat:@"Boundary+%08X%08X", arc4random(), arc4random()];
    NSMutableString *topStr = [NSMutableString string];
    [topStr appendFormat:@"--%@\r\n",boundary];
    
//    [topStr appendFormat:@"Content-Disposition: form-data; name=\"FileName\"\r\n"];
//    [topStr appendFormat:@"Content-Type: text/plain; charset=\"utf-8\"\r\n\r\n"];
//    [topStr appendFormat:@"%@.jpg\r\n",@"image"];
//    [topStr appendFormat:@"--%@\r\n",boundary];
    
    [topStr appendFormat:@"Content-Disposition: form-data; name=\"file\"; filename=\"%@.jpg\"\r\n",@"image"];
    [topStr appendFormat:@"Content-Type: image/jpeg\r\n\r\n"];
    
    NSMutableData *body = [NSMutableData data];
    [body appendData:[topStr dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:data];
    NSString *endStr = [NSString stringWithFormat:@"\r\n--%@--\r\n",boundary];
    [body appendData:[endStr dataUsingEncoding:NSUTF8StringEncoding]];
    
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:url] cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:30];
    request.HTTPMethod = @"POST";
    request.HTTPBody = body;
    [request setValue:[NSString stringWithFormat:@"%lu", (unsigned long)body.length] forHTTPHeaderField:@"Content-Length"];
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; charset=utf-8;boundary=%@",boundary];
    [request setValue:contentType forHTTPHeaderField:@"Content-Type"];
    
    NSURLSessionDataTask *task = [[NSURLSession sharedSession]dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        dispatch_async(dispatch_get_main_queue(), ^{
            if (error) {
                NSLog(@"[error localizedDescription] == %@",[error localizedDescription]);
            }else{
                NSLog(@" 图片上传 响应结果:%@", response);
                id rdic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
                NSLog(@"图片上传 返回数据:\n%@",rdic);
                
            }
        });
    }];
    [task resume];
    
}

请求头（图片来自Charles 4.5.6）

5B92E8E5-4553-40B9-8894-B4B1765CC40A.png