How do I load an image from HTML to Flask?

if request.method=="PUT":
        for f in request.files.getlist("Files"): #<---- note 1
  , f.filename)) 
        return jsonify({"result": "res"}), 200 #status code is only thing important here

const file_loader = document.getElementById("file_loader");

file_loader.onchange = async function(e){   
    alert("Upload started")
    let sending = new FormData(); //creates form data object

//this for loop adds all files you selected to a form object
    for (let i = 0; i < file_loader.files.length; i++) {        
        sending.append("Files", file_loader.files[i]);   //<---- note 1 

//this part just sends all the files to server
    const podaci = await fetch(url_filesistem, {
        method: "PUT",
        body: sending,        
    .then((response) => response.json())
    .then((pod) => {return pod;}); 
//removing all selected files from an input, so every time you want to select files
//its just those files, not ones previously selected
    while (file_loader.length > 0) {
    alert("Finnished uploading")