1. 将图片转换为Base64编码，POST上传。PHP将Base64解码为二进制，再写出文件。缺点：不能上传较大的图片

// iOS(Swift)
func upload(image: UIImage, url: String) {
    let imageData = UIImageJPEGRepresentation(image, 0.3) // 将图片转换成jpeg格式的NSData，压缩到0.3
    let imageStr = imageData?.base64EncodedStringWithOptions(.Encoding64CharacterLineLength) // 将图片转换为base64字符串
    let params: NSDictionary = ["file": imageStr!]
    let manager = AFHTTPRequestOperationManager()

    // 采用POST的方式上传，因为POST对长度没有限制
    manager.POST(url, parameters: params, success: { (_: AFHTTPRequestOperation!, response: AnyObject!) in
        // 成功
    }) { (_: AFHTTPRequestOperation!, _: NSError!) in
        // 失败
    }
}

<?php
header('Content-type: text/json; charset=UTF-8');

$base64 = $_POST["file"]; // 得到参数
$img = base64_decode($base64); // 将格式为base64的字符串解码
$path = "md5(uniqid(rand()))".".jpg"; // 产生随机唯一的名字作为文件名
file_put_contents($path, $img); // 将图片保存到相应位置
?>

2.AFNetworking上传，PHP端通过正常接收网页上传方法来接收图片

static func uploadPortrait(image: UIImage, url: String) {
    let manager = AFHTTPRequestOperationManager()

    // fromData: AFN封装好的http header类，可以添加请求体
    manager.POST(url, parameters: [:], constructingBodyWithBlock: { (fromData: AFMultipartFormData!) in
        let pngData = UIImagePNGRepresentation(image)
        // name必须和后台PHP接收的参数名相同($_FILES["file"])
        // fileName为图片名
        fromData.appendPartWithFileData(pngData, name: "file", fileName: "image.png", mimeType: "image/png")      

        // let jpegData = UIImageJPEGRepresentation(image, 0.3)
        // fromData.appendPartWithFileData(jpegData, name: "file", fileName: "image.jpg", mimeType: "image/jpeg")
    }, success: { (operation: AFHTTPRequestOperation!, response: AnyObject!) in
        // 成功
    }) { (operation: AFHTTPRequestOperation!, error: NSError!) in
        // 失败
    }   
}

<?php
header('Content-type: text/json; charset=UTF-8' );

/**
 * $_FILES 文件上传变量，是一个二维数组，第一维保存上传的文件的数组，第二维保存文件的属性，包括类型、大小等
 * 要实现上传文件，必须修改权限为加入可写 chmod -R 777 目标目录
 */

// 文件类型限制
// "file"名字必须和iOS客户端上传的name一致
if (($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/png")
|| ($_FILES["file"]["type"] == "image/pjpeg"))
// && ($_FILES["file"]["size"] < 20000)) // 小于20k
{
    if ($_FILES["file"]["error"] > 0) {
        echo $_FILES["file"]["error"]; // 错误代码
    } else {           
        $fillname = $_FILES['file']['name']; // 得到文件全名
        $dotArray = explode('.', $fillname); // 以.分割字符串，得到数组
        $type = end($dotArray); // 得到最后一个元素：文件后缀

        $path = "../portrait/".md5(uniqid(rand())).'.'.$type; // 产生随机唯一的名字

        move_uploaded_file( // 从临时目录复制到目标目录
          $_FILES["file"]["tmp_name"], // 存储在服务器的文件的临时副本的名称
          $path);

        echo "成功";
    } 
} else {
    echo "文件类型不正确";
}
?>

3.将图片封装在Http的请求报文中的请求体（body）中上传。也是AFN上传的原理

// 使用OC封装
#import <UIKit/UIKit.h>
@interface RequestPostUploadHelper : NSObject
+ (NSMutableURLRequest *)uploadImage:(NSString*)url uploadImage:(UIImage *)uploadImage params:(NSMutableDictionary *)params;
@end

#import "RequestPostUploadHelper.h"
@implementation RequestPostUploadHelper
+ (NSMutableURLRequest *)uploadImage:(NSString*)url uploadImage:(UIImage *)uploadImage params:(NSMutableDictionary *)params {
    [params setObject:uploadImage forKey:@"file"];

    //分界线的标识符
    NSString *TWITTERFON_FORM_BOUNDARY = @"AaB03x";
    //根据url初始化request
    NSMutableURLRequest* request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]
                                                           cachePolicy:NSURLRequestReloadIgnoringLocalCacheData
                                                       timeoutInterval:10];
    //分界线 --AaB03x
    NSString *MPboundary=[[NSString alloc]initWithFormat:@"--%@",TWITTERFON_FORM_BOUNDARY];
    //结束符 AaB03x--
    NSString *endMPboundary=[[NSString alloc]initWithFormat:@"%@--",MPboundary];
    //要上传的图片
    UIImage *image=[params objectForKey:@"file"];
    //得到图片的data
    NSData* data = UIImagePNGRepresentation(image);
    //http body的字符串
    NSMutableString *body=[[NSMutableString alloc]init];
    //参数的集合的所有key的集合
    NSArray *keys= [params allKeys];

    //遍历keys
    for(int i = 0; i < [keys count]; i++)
    {
        //得到当前key
        NSString *key = [keys objectAtIndex:i];
        //如果key不是file，说明value是字符类型，比如name：Boris
        if(![key isEqualToString:@"file"])
        {
            //添加分界线，换行
            [body appendFormat:@"%@\r\n",MPboundary];
            //添加字段名称，换2行
            [body appendFormat:@"Content-Disposition: form-data; name=\"%@\"\r\n\r\n",key];
            //添加字段的值
            [body appendFormat:@"%@\r\n",[params objectForKey:key]];
        }
    }

    ////添加分界线，换行
    [body appendFormat:@"%@\r\n",MPboundary];
    //声明file字段，文件名为image.png
    [body appendFormat:@"Content-Disposition: form-data; name=\"file\"; filename=\"image.png\"\r\n"];
    //声明上传文件的格式
    [body appendFormat:@"Content-Type: image/png\r\n\r\n"];

    //声明结束符：--AaB03x--
    NSString *end=[[NSString alloc] initWithFormat:@"\r\n%@",endMPboundary];
    //声明myRequestData，用来放入http body
    NSMutableData *myRequestData = [NSMutableData data];
    //将body字符串转化为UTF8格式的二进制
    [myRequestData appendData:[body dataUsingEncoding:NSUTF8StringEncoding]];
    //将image的data加入
    [myRequestData appendData:data];
    //加入结束符--AaB03x--
    [myRequestData appendData:[end dataUsingEncoding:NSUTF8StringEncoding]];

    //设置HTTPHeader中Content-Type的值
    NSString *content=[[NSString alloc]initWithFormat:@"multipart/form-data; boundary=%@",TWITTERFON_FORM_BOUNDARY];
    //设置HTTPHeader
    [request setValue:content forHTTPHeaderField:@"Content-Type"];
    //设置Content-Length
    [request setValue:[NSString stringWithFormat:@"%d", [myRequestData length]] forHTTPHeaderField:@"Content-Length"];
    //设置http body
    [request setHTTPBody:myRequestData];
    //http method
    [request setHTTPMethod:@"POST"];

    return request;
}
@end

// 使用
// Swift
static func uploadPortrait(image: UIImage, url:String) {
    // 使用
    let request = RequestPostUploadHelper.uploadImage(url, uploadImage: image, params: [:])
    // 异步网络请求
    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue()) { (response: NSURLResponse?, data: NSData?, error: NSError?) in
        if error != nil {
            // 失败
        } else {
            // 成功
        }
    }
}

<?php
// PHP代码和上一步相同
?>

4.iOS图片转换为NSData，通过POST上传。PHP接收POST参数，将NSData的16进制编码转换为PHP支持的二进制，再写出文件保存

5.二进制POST上传。PHP直接将数据保存为图片