After lots of searching based on several sources, I found a way to send a picture stored in JavaScript in a POST request to another screen as well as loading the picture directly from memory into another HTML page.

First, in order to send a picture from JavaScript, I created a form with a POST method just for this image:

 <form action="/CropperScreen" method="POST" id="ImageForm" enctype="multipart/form-data">
            <input name="imageFile" id="imageFile" hidden type="file"/>
            <input hidden type="submit">
    </form>

Afterwards, I get a file input responsible for sumbiting the image and store it in a variable:

const fileInput = document.querySelector('#imageFile');

I then fill the file input with the file and file information:

// Get your file ready
            const myFileContent = [fileURL];
            const myFileName = 'test.png';
            const myFile = new File(myFileContent, myFileName);

            // Create a data transfer object. Similar to what you get from a `drop` event as `event.dataTransfer`
            const dataTransfer = new DataTransfer();

            // Add your file to the file list of the object
            dataTransfer.items.add(file);

            // Save the file list to a new variable
            const fileList = dataTransfer.files;

            // Set your input `files` to the file list
            fileInput.files = fileList;

Finally, I locate the form and submit it by JavaScript code:

document.getElementById("ImageForm").requestSubmit();

Some of this work was based on:
https://dev.to/code_rabbi/programmatically-setting-file-inputs-in-javascript-2p7i

Now in order to display it onto another HTML screen, I first receive it from the routed action I specified in the form and store the image in a variable:

@app.route('/CropperScreen',methods=['GET','POST'])
def cropper_screen():
    if request.method == "POST":
        imageFile = request.files.get('imageFile', '')

I then create an BYTESIO() object, and use the save() function in the “image” object to store the image as a byte buffer:

imageIO = io.BytesIO()
imageFile.save(imageIO)

The buffer is converted to a byte stream, converted to ASCII and converted to base64 which is then parsed pased on the urllib library. THe resolted is added to a special uri syntax and sent to the HTML page:

uri = 'data:image/png;base64,' + urllib.parse.quote(base64.b64encode(imageIO.getvalue()).decode('ascii'))

        return render_template('CropperScreen.html',uri=uri)

Finally, in the HTML page, the uri syntax is used in the “src” section of an img tag like this:

<img id="image" src="{{ uri }}">

The buffer and uri idea was based on this answer:
/a/70849754/17870878