Failed to upload image over custom server

Using web service, I was trying to upload image to web server. At present I want to upload profile picture to custom server but in this always, I was getting this error in Unity editor.

For this, I was using following code:

 void Start ()
 {
     StartCoroutine (UploadPNG ());
 }
 
 IEnumerator UploadPNG ()
 {
     // We should only read the screen after all rendering is complete
     yield return new WaitForEndOfFrame ();
 
     // Create a texture the size of the screen, RGB24 format
     int width = Screen.width;
     int height = Screen.height;
     var tex = new Texture2D (width, height, TextureFormat.RGB24, false);
 
     // Read screen contents into the texture
     tex.ReadPixels (new Rect (0, 0, width, height), 0, 0);
     tex.Apply ();
 
     // Encode texture into PNG
     byte[] bytes = tex.EncodeToPNG ();
     Destroy (tex);
 
     // Create a Web Form
     WWWForm form = new WWWForm ();
     form.AddBinaryData ("profile_pic", bytes, "screenShot.png", "image/png");
 
     // Upload to a cgi script
     WWW w = new WWW (screenShotURL, form);
     yield return w;
     if (!string.IsNullOrEmpty (w.error)) {
         print (w.error);
     } else {
         print ("Finished Uploading Screenshot");
     }
 }
 

This is similar code that I found from here: WWWForm

As well screenshot after running url in PostMan.

Here is actual url to test:

 private string screenShotURL = "http://photo-competition.igts.co.in/restapi/image_upload_demo_ws";

Please suggest me at which place I have done mistake.

EDIT: Following two link give you source code used from PHP side.

Image Upload Part-1

Image Upload Part-2