Post photo from phone gallary to Api using retroft Android

Question

i have project and i need to post photo that chose from user to Api , and in another activity i have to get the photo , my question is how i can post the photo?? and what the column type in api should be ??? i using retroft and all the project and i need to post photo in retroft ? this how i get the photo from user and i need to post it !

       buttonLoadImage.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            Intent i = new Intent(Intent.ACTION_PICK,android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
            startActivityForResult(i, RESULT_LOAD_IMAGE);
        }
    });
    if (shouldAskPermission() == true)
    {
        String[] perms = {"android.permission.READ_EXTERNAL_STORAGE"};
        int permsRequestCode = 200;
        requestPermissions(perms, permsRequestCode);
    }
    s = (Button) findViewById(R.id.button);
    s.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Save();
        }
    });
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK && null != data) {
        Uri selectedImage = data.getData();
        String[] filePathColumn = { MediaStore.Images.Media.DATA };
        Cursor cursor = getContentResolver().query(selectedImage,filePathColumn, null, null, null);
        cursor.moveToFirst();
        int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
         picturePath = cursor.getString(columnIndex);
        cursor.close();
        ImageView imageView = (ImageView) findViewById(R.id.imgView);
        imageView.setImageBitmap(BitmapFactory.decodeFile(picturePath));
        Log.d("image",picturePath+"");

    }
}
private boolean shouldAskPermission(){
    return(Build.VERSION.SDK_INT> Build.VERSION_CODES.LOLLIPOP_MR1);
}