参考 tesseract-ocr vision api を使ったサンプル、vb.net(framework4.5)exe

Imports System
Imports System.Net.Http.Headers
Imports System.Text
Imports System.Net.Http
Imports System.Web
Module Module2
  Sub mainrtn()
      Call MakeRequest()
  End Sub
  Async Sub MakeRequest()
      Dim client = New HttpClient()
      'Dim queryString = HttpUtility.ParseQueryString(String.Empty)
      '----------------------------------------
      '呼び出しＵＲＩの設定
      '----------------------------------------
      Dim queryString = HttpUtility.ParseQueryString("language=unk")
      ''''client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", "{subscription key}")
      client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx")
      ''''option param 'queryString("visualFeatures") = "Categories"
      ''''option param 'queryString("details") = "{string}"
      ''''Dim Uri As String = "https://api.projectoxford.ai/vision/v1.0/analyze?" & queryString.ToString
      Dim Uri As String = "https://api.projectoxford.ai/vision/v1.0/ocr?" & queryString.ToString
      '----------------------------------------
      'パラメータ指定
      '----------------------------------------
      ''''Dim byteData As Byte() = Encoding.UTF8.GetBytes("{body}")
      ''''Dim byteData As Byte() = Encoding.UTF8.GetBytes("{""Url"":""http://contoso.com/images/test1.jpg""}")
      Dim byteData As Byte() = Encoding.UTF8.GetBytes("{""Url"":""http://sample.jp/sample.jpg""}")
      Dim response As HttpResponseMessage
      Dim contentsstring As String
      Using content As New ByteArrayContent(byteData)
          ''''content.Headers.ContentType = New MediaTypeHeaderValue("< your content type, i.e. application/json >")
          content.Headers.ContentType = New MediaTypeHeaderValue("application/json")
          '----------------------------------------
          '非同期メソッドの待ち合わせ
          '----------------------------------------
          response = Await client.PostAsync(Uri, content)
          contentsstring = Await response.Content.ReadAsStringAsync
      End Using
      '----------------------------------------
      '結果判定
      '----------------------------------------
      If response.StatusCode = "200" Then
          MsgBox(contentsstring)
      End If
  End Sub
End Module