//global variables that can be used by ALL the function son this page.
var inputs;
var imgFalse = 'img/checkbox_off.jpg';
var imgTrue =  'img/checkbox_on.jpg';

//this function runs when the page is loaded, put all your other onload stuff in here too.
function init() { replaceChecks(); }

function replaceChecks()
{
    inputs = document.getElementsByTagName('input');
    for(var i=0; i < inputs.length; i++)
    {
        if(inputs[i].getAttribute('type') == 'checkbox')
        {
            var img = document.createElement('img');
            var iName = inputs[i].getAttribute('name');
            
            if(inputs[i].checked)
            {
                    img.src = imgTrue;
            } else {
                    img.src = imgFalse;
            }
            
            img.id = 'checkImage_' + iName;
            img.onclick = new Function('checkChange('+ i +',\''+ iName +'\')');
            img.className = 'checkbox_image';
            
            inputs[i].parentNode.insertBefore(img, inputs[i]);
            inputs[i].style.display='none';
        }
    }
}

//change the checkbox status and the replacement image
function checkChange(i, iName)
{
    if(inputs[i].checked)
    {
        inputs[i].checked = '';
        document.getElementById('checkImage_' + iName).src=imgFalse;
    } else {
        inputs[i].checked = 'checked';
        document.getElementById('checkImage_' + iName).src=imgTrue;
    }
}

function toggleCheckbox(e)
{
    if (document.getElementById(e).checked)
    {
        document.getElementById(e).checked = false;
        document.getElementById('checkImage_' + e).src=imgFalse;
    } else {
        document.getElementById(e).checked = true;
        document.getElementById('checkImage_' + e).src=imgTrue;
    }
    
}

// reset checkboxes bij "herstel(len)" 
function resetCheckboxes(e)
{
    document.getElementById('checkImage_' + e).src =imgFalse;
}

window.onload = init;