Ionic POST api with params and file image

Ionic Framework ionic-v3
1

I am beginner of ionic3, I have a api with some params and image to send back to server, i have crop the image with below code:

    this.camera.getPicture(cameraOptions)
    .then(file_uri => {
       this.crop.crop(file_uri, {quality: 100})
       .then(
          newImage => {console.log('new image path is: ' + newImage);
          this.imageSrc = newImage},
          error => console.error('Error cropping image', error)
       );
    },
    err => console.log(err));

and my calling api code is:

let opt: RequestOptions;
let myHeaders: Headers = new Headers;

myHeaders.set('Accept', 'application/json; charset=utf-8');
myHeaders.append('Content-type', 'application/json; charset=utf-8');
opt = new RequestOptions({
  headers: myHeaders
})
return new Promise((resolve, reject) => {
console.log(apiUrl);
  this.http.post(apiUrl+'register?email='+email+'&userImg='+userImg, opt)
  .map(res => res.json())
  .subscribe(data => {
    this.data = data;
    resolve(this.data);
  },(err) => {
    reject(err);
  });
});

above email is the param & userImg is the image that I want to send back to server. My Question is how can I put this cropped image with other params to call the api? Thanks a lot. Hope for a reply~Thanks again.