Error sending and saving AJAX and PHP image

In the script I have the camera on and then The Code that the image takes on a canvas. I see that it returns a base64 I remove ( data:image/jpeg;base64, ) that brings the text.

I'm trying:

The code I have is the following to see what I'm doing wrong:

JavaScript

window.addEventListener('load');



function encender() {
  //declara variables
  var button = this;
  button.innerHTML = 'Tomar Foto';
  var video = document.querySelector('#video'),
    canvas = document.querySelector('#canvas'),
    btn = document.querySelector('#camara'),
    img = document.querySelector('#imagen');

  //acceso a la camara
  navigator.getUserMedia = (
    navigator.getUserMedia ||
    navigator.webkitGetUserMedia ||
    navigator.mozGetUserMedia ||
    navigator.msGetUserMedia
  );

  //validar que encontro
  if (navigator.getUserMedia) {
    //reproduce el video
    navigator.getUserMedia({
      video: true
    }, function(stream) {
      video.src = window.URL.createObjectURL(stream); //lee la camara
      video.play(); //reproduce el video
    }, function(e) {
      console.log(e);
    })

  } else {
    alert('No se acepta el video en tu navegador');
  }

  video.addEventListener('loadedmetadata', function() {
    canvas.width = video.videoWidth;
    canvas.height = video.videoHeight;
  }, false);

  btn.addEventListener('click', function(e) {
    e.preventDefault();
    canvas.getContext('2d').drawImage(video, 0, 0);
    var imgData = canvas.toDataURL('image/jpeg');
    var imagenData = canvas.toDataURL('image/jpeg');
    var imagenData = imagenData.replace(/^data:image\/jpeg;base64,/, "+"); //Quito data:image/jpeg;base64 para convertir imagen

    $.ajax({
      url: 'saveFile.php',
      data: {
        imagenData: imagenData
      },
      method: 'post',
      success: function(data) {
        alert("Imagen guardada en servidor");
      }

    });

    $("#operation-driver_identification_file").val(imagenData);
    img.setAttribute('src', imgData);



  });

}

PHP:

<?php $this->registerJsFile("@web/js/camara.js");
?><?=$form->field($model, 'driver_identification_file')->textInput(['disabled'=> true]);
?><?php
/* saveFile.php */

//Obtener variable POST e desemcriptarla
$img=$_POST['imagenData'];
//$img = str_replace('data:image/png;base64,', '', $img); //este cambio en el JS
//$img = str_replace(' ', '+', $img);
$data=base64_decode($img);
$im=imagecreatefromstring($data); //convertir text a imagen
if ($im !==false) {
  imagejpeg($im, 'capture/'); //guardar a server 
  imagedestroy($im); //liberar memoria  
  echo 'Todo salio bien tu imagen ha sido guardada';
}

else {
  echo 'Un error ocurrio al convertir la imagen.';
}

HTML:

<video id="video"></video>
<canvas id="canvas"></canvas><br>

<input type="button" value="Encender" onclick="encender()" />
<button id="camara">Take photo</button>