c# .NET multipart/form-data Upload A File

I want to create an application to automaticly upload a file to googles SearchbyImage-tool https://www.google.de/searchbyimage/upload

Google is using a multipart/form-data for submitting the file, something like that:

Content-Type: multipart/form-data; boundary=---------------------------265001916915724
Content-Length: 9989
-----------------------------265001916915724
Content-Disposition: form-data; name="image_url"


-----------------------------265001916915724
Content-Disposition: form-data; name="encoded_image"; filename=""
Content-Type: application/octet-stream


-----------------------------265001916915724
Content-Disposition: form-data; name="image_content"

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