function SignatureShow(checkbox,imageId) {
    var image = document.getElementById(imageId);
    if (image) {
        if (checkbox.checked)
            document.getElementById(imageId).style.visibility = 'visible';
        else
            document.getElementById(imageId).style.visibility = 'hidden';
    }
}

function SignatureRequired(source, args) 
{ 
     var isvalid = document.getElementById(source.id + '_signature').checked; 
     if (!isvalid) document.getElementById(source.id + '_signature').focus();
     args.IsValid = isvalid;
}