Pass Value from JS Function to Blade View Form

I need to capture a screenshot from an HTML element and then upload that screenshot as an image file. I am using html2canvas to create a JavaScript function that will download the image with an onClick function. The capture screenshot function works to download "onClick".

I need to pass the value of that function to the blade form (laravaelcollective/html).

//Blade form:  
{!! Form::open(['method'=>'POST', 'action' => 'AdminFloorsController@store', 'files'=>true]) !!}

            <div class="form-group">
                {!! Form::hidden('photo_id', null, ['class' => 'form-control']) !!}
            </div>

            <div class="form-group">
                {!! Form::submit('Create Property', ['onClick' => 'takeScreenShot()', 'class' => 'btn btn-primary']) !!}
            </div>

            {!! Form::close() !!}  

//JavaScript function  
    <script type="text/javascript">
        window.takeScreenShot = function() {

            html2canvas(document.getElementById("screenshot"), {
                onrendered: function(canvas) {
                    var screenshot = canvas.toDataURL("image/png");

                   download(screenshot, "image_captured", "image/png");
                },
            });
        }
    </script>