function validate(formCheck) //Function with a parameter representing a form name.
{

  var mail=formCheck.custom_field_three.value
var apos=mail.indexOf("@"); 
var dotpos=mail.lastIndexOf(".");
var lastpos=mail.length-1;
if (apos<1 || dotpos-apos<2 || lastpos-dotpos>3 || lastpos-dotpos<2) 

    {
        alert("Please type a valid email:");
        formCheck.custom_field_three.focus(); 
        return false;
    }

    if (formCheck.custom_field_one.value =="")
    {
        alert("Please provide your name:"); 
        formCheck.custom_field_one.focus();
        return false;
    }


    if (!formCheck.custom_field_two.checked)
    {
        alert("You must confirm copyright:"); 
        return false;
    }

    if (formCheck.userfile.value =="")
    {
        alert("Please select a file to upload:"); 
        formCheck.custom_field_one.focus();
        return false;
    }


    if (formCheck.caption.value =="")
    {
        alert("Please provide an image description:"); 
        formCheck.custom_field_one.focus();
        return false;
    }


   return true;

}