1) Copy and Past at the top of the body :
    <script>
       function setInputVal(id, value) {
           let input = document.getElementById(id);
           input.value = value;
       }
    </script>

2) Call the function inside onclick event :
    <img
        src="../images/scarpa.jpg"
        width="612"
        height="334"
        border="0"
        onclick="setInputVal('descriptionpartvalue', 'toebox')"
        href="javascript:void(0)"
        usemap="#map"
    />

    setInputVal function receives 2 arguments:
        i ) id
        ii) value

    `id` means id attribute of that input tag whose value you want to change.
     if <input id="abc" name="xyz"/> is an input, then `abc` will be it's id

     `value` means which value you want to set in that input field.
     if you want to set `toe` as value of that input, then you've to
     pass `toe` as second argument

3) After `onclick` attribute you must replace `href` with `href="javascript:void(0)"` otherwise your
   page will be reloaded!