如何通过微信网页版 web 接口中如何发送图片？

在分析微信网页版，想发送图片，看了一下，微信通过下面的 multipart post 上传图片到服务器，但奇怪的是没看到图片的 2 进制啊，怎么上传的呢，

Request URL:https://file.wx.qq.com/cgi-bin/mmwebwx-bin/webwxuploadmedia?f=json

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Content-Disposition: form-data; name="id"

WU_FILE_1
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="name"

[email protected]
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="type"

image/png
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="lastModifiedDate"

Sat May 09 2015 15:04:48 GMT+0800 (CST)
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="size"

4773
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="mediatype"

pic
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="uploadmediarequest"

{"BaseRequest":{"Uin":1324081430,"Sid":"kLiK1rL2q8hQoYN9","Skey":"@crypt_c4afdbd8_c10795dc7bdec30d21267fc1284f4050","DeviceID":"e690928520634770"},"ClientMediaId":1453465224337,"TotalLen":4773,"StartPos":0,"DataLen":4773,"MediaType":4}
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="webwx_data_ticket"

AQdQY+GQOJsNhTQRxBBFFOhZ
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="pass_ticket"

eGahUyL63xtx3P6tKM30iZkKlXNpypJcvv+0K5fwRBEJYerp4g290NooKh38Z1Vc
------WebKitFormBoundary4t32GXtXdZesZUzK
Content-Disposition: form-data; name="filename"; filename="[email protected]";
Content-Type: image/png


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