function showOverlay(picture) {

    var xScroll, yScroll;

    if (window.innerHeight && window.scrollMaxY) {
        xScroll = window.innerWidth + window.scrollMaxX;
        yScroll = window.innerHeight + window.scrollMaxY;
    } else if (document.body.scrollHeight > document.body.offsetHeight){ // all but Explorer Mac
        xScroll = document.body.scrollWidth;
        yScroll = document.body.scrollHeight;
    } else { // Explorer Mac...would also work in Explorer 6 Strict, Mozilla and Safari
        xScroll = document.body.offsetWidth;
        yScroll = document.body.offsetHeight;
    }

    var windowWidth, windowHeight;

    if (self.innerHeight) { // all except Explorer
        if(document.documentElement.clientWidth){
            windowWidth = document.documentElement.clientWidth;
        } else {
            windowWidth = self.innerWidth;
        }
        windowHeight = self.innerHeight;
    } else if (document.documentElement && document.documentElement.clientHeight) { // Explorer 6 Strict Mode
        windowWidth = document.documentElement.clientWidth;
        windowHeight = document.documentElement.clientHeight;
    } else if (document.body) { // other Explorers
        windowWidth = document.body.clientWidth;
        windowHeight = document.body.clientHeight;
    }

    // for small pages with total height less then height of the viewport
    if(yScroll < windowHeight){
        pageHeight = windowHeight;
    } else {
        pageHeight = yScroll;
    }

    // for small pages with total width less then width of the viewport
    if(xScroll < windowWidth){
        pageWidth = xScroll;
    } else {
        pageWidth = windowWidth;
    }

    document.getElementById('overlay').style.width = pageWidth+"px";
    document.getElementById('overlay').style.height = pageHeight+"px";

    document.getElementById('pictureBox').innerHTML = '<div id="pictureBoxContent"><img src="/sites/all/themes/bm_fr/graphics/'+picture+'" /></div><div class="pictureBoxClose" onclick="closeOverlay();">[ Fermer la fen&ecirc;tre ]</div>';

    document.getElementById('overlay').style.display = "block";
    document.getElementById('pictureBox').style.display = "block";

    if (document.getElementById('overlay').addEventListener){
        document.getElementById('overlay').addEventListener('click', closeOverlay, false);
    } else if (document.getElementById('overlay').attachEvent){
        document.getElementById('overlay').attachEvent('onclick', closeOverlay);
    }
}

function closeOverlay() {
    document.getElementById('overlay').style.display = "none";
    document.getElementById('pictureBox').style.display = "none";
}