var minpwlength = 4;
    var fairpwlength = 7;
    
    var STRENGTH_SHORT = 0;  // less than minpwlength 
    var STRENGTH_WEAK = 1;  // less than fairpwlength
    var STRENGTH_FAIR = 2;  // fairpwlength or over, no numbers
    var STRENGTH_STRONG = 3; // fairpwlength or over with at least one number
    
    img0 = new Image(); 
    img1 = new Image();
    img2 = new Image();
    img3 = new Image();
    
    img0.src = 'sys_images/tooshort.jpg';
    img1.src = 'sys_images/fair.jpg';
    img2.src = 'sys_images/medium.jpg';
    img3.src = 'sys_images/strong.jpg';
    
    var strengthlevel = 0;
    
    var strengthimages = Array( img0.src,
                                img1.src,
                                img2.src,
                                img3.src );
    
    function updatestrength( pw ) {
        if( istoosmall( pw ) ) {
            strengthlevel = STRENGTH_SHORT;
        }
        else if( !isfair( pw ) ) { 
            strengthlevel = STRENGTH_WEAK;
        }    
        else if( hasnum( pw ) ) {
            strengthlevel = STRENGTH_STRONG;
        }
        else {
            strengthlevel = STRENGTH_FAIR;
        }
        //document.getElementById( 'strength' ).src = strengthimages[ strengthlevel ];
        document.getElementById('strength').innerHTML = "<img src='"+strengthimages[ strengthlevel ]+"' alt='Strength' height='25'>";
    }
    
    function isfair( pw ) {
        if( pw.length < fairpwlength ) {
            return false;
        }
        else { 
            return true;
        }
    }
    
    function istoosmall( pw ) {
    
        if( pw.length < minpwlength ) {
            return true;
        }
        else {
            return false;
        }
    }
    
    function hasnum( pw ) {
        var hasnum = false;
        for( var counter = 0; counter < pw.length; counter ++ ) {
            if( !isNaN( pw.charAt( counter ) ) ) {
                hasnum = true;
            }
        }
        return hasnum;
    
    }