Send DataURl to webservice using Json/jquery

Send DataURl to webservice using Json/jquery

Hi,
I am trying to save Base64 data in to database.
But I am not able to send dataUrl to my .asmx file.
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Jquery
======
function UploadUserPhoto() {                
                var Mycanvas = document.getElementById("tempCanvas");
                var dataURL = Mycanvas.toDataURL("image/png");               
                
                $.ajax({
                    url: "LP18WS.asmx/UploadPhoto",
                    contentType: "application/json; charset=utf-8",
                    data: {
                        Base64String: "\'" + dataURL + "\'"
                    },
                    dataType: "json",
                    success: function (msg) {
                        alert(msg.d);
                        
                    },
                    error: function (msg) {
                        alert(msg + '\n' + xhr.responseText);
                    },
                });
}

Webservice(LP18WS.asmx)
======================
[WebMethod(EnableSession = true)]
[ScriptMethod(ResponseFormat = ResponseFormat.Json,  UseHttpGet = true)]
public string UploadPhoto(string Base64String)
{
   string message = "";
    //code to save data url in database            
   return message;
}

=============================
But it is not sending the dataurl. If I put some other string instead of dataurl it is working.
Why this dataurl can't send?. Can any one guid me?