check = []; //this is an array that stores all the true/false values for each checkbox

function checkBox(id) { 
if (document.getElementById('inputCheck' + id).value == 'off') { 
document.getElementById('imgCheck' + id).src = 'images/checked.jpg'; //change the image 
document.getElementById('inputCheck' + id).value = 'ok'; //change the field value 
} else { 
document.getElementById('imgCheck' + id).src = 'images/unchecked.jpg'; //change the image 
document.getElementById('inputCheck' + id).value = 'off'; //change the field value 
} 
}