var cachePicCheckbox, cachePicCheckboxChek;

function createCheckBoxImages(FNameDef, FnameChek, pic)  //createCheckBoxImages("checkbox.PNG", "checkboxCheked.PNG", document.picCheckbox);  
{
    cachePicCheckbox = new Image();
    cachePicCheckboxChek = new Image();
    cachePicCheckbox.src = FNameDef; 
    cachePicCheckboxChek.src = FnameChek; 
}

function checkboxChange(pic, hiddenField)   // checkboxChange(document.picCheckbox, document.loginCheckActionForm.hiddenCheckField) 
{
   if (pic.src == cachePicCheckbox.src)
    {
        hiddenField.value = 1;
        pic.src = cachePicCheckboxChek.src;
    }
    else
    {
        hiddenField.value = 0;
        pic.src = cachePicCheckbox.src;
    }
}