imgCaptcha.Source = new BitmapImage(new Uri("http://localhost:2918/AntiBotImage.ashx"));
<endpoint address="http://localhost:2918/CaptchaService.asmx" binding="basicHttpBinding" bindingConfiguration="CaptchaServiceSoap" contract="CaptchaServiceReference.CaptchaServiceSoap" name="CaptchaServiceSoap" />