Share screenshot on FB without SDK?

Greetings,

I'm trying to take a screenshot of the game and have the player be able to post it on their Facebook. I found a simple script that uses Facebook feed to share an image, given the URL of the image so the image has to be uploaded somewhere first for it to be shared.

The function works fine, however; I don't want to upload the picture to anywhere cause it's just a temporary thing it would be nice if I could pass the image data in the URL directly. So, I tried saving the picture to disk, and used "file://image_path.jpg" as the picture link.

     public static void ShareOnFB()
     {
         int width = Screen.width;
         int height = Screen.height;
         var texture = new Texture2D(width, height, TextureFormat.RGBA32, false);
         texture.ReadPixels(new Rect(0, 0, width, height), 0, 0);
         texture.Apply();
 
         byte[] screenshot = texture.EncodeToJPG();
         string savepath = Application.persistentDataPath + "/Screenshot.jpg";
         File.WriteAllBytes(savepath, screenshot);
 
         string AppID = "APP ID NUMBER";
         string Link = "https://play.google.com";
         string Name = "Test Picture Share";
         string Caption = "Yo I got a cool score";
         string Description = "Enjoy this game";
         string Picture = "file://" + savepath;
 
         Application.OpenURL("https://www.facebook.com/dialog/feed?" + "app_id=" + AppID + "&link=" + Link + "&picture=" + Picture + "&name=" + ReplaceSpace(Name) + "&caption=" + ReplaceSpace(Caption) + "&description=" + ReplaceSpace(Description) + "&redirect_uri=https://facebook.com/");

     }

However I'm getting an error from Facebook: "picture is not properly formatted"

Any idea how I can get this thing to work?

And if I must upload the image somewhere, I was looking how I would use imgur or something but nothing seems to be straight-forward. Is there an easy way/website that I could temporarily dump images to? I found a lot of websites but I'm not sure how to upload to them via code from Unity.

Thanks.

@Bunny83