pic1 = new Image();
pic1.src = "images/mainImg/image1.jpg";
pic2 = new Image();
pic2.src = "images/mainImg/image2.jpg";
pic3 = new Image();
pic3.src = "images/mainImg/image3.jpg";
pic4 = new Image();
pic4.src = "images/mainImg/image4.jpg";
pic5 = new Image();
pic5.src = "images/mainImg/image5.jpg";
pic6 = new Image();
pic6.src = "images/mainImg/image6.jpg";

function changeImg1() {
    document.getElementById("mainImg").style.backgroundImage = "url('images/mainImg/image2.jpg')";
    setTimeout("changeImg2()", 5000);
}

function changeImg2() {
    document.getElementById("mainImg").style.backgroundImage = "url('images/mainImg/image3.jpg')";
    setTimeout("changeImg3()", 5000);
}

function changeImg3() {
    document.getElementById("mainImg").style.backgroundImage = "url('images/mainImg/image4.jpg')";
    setTimeout("changeImg4()", 5000);
}

function changeImg4() {
    document.getElementById("mainImg").style.backgroundImage = "url('images/mainImg/image5.jpg')";
    setTimeout("changeImg5()", 5000);
}

function changeImg5() {
    document.getElementById("mainImg").style.backgroundImage = "url('images/mainImg/image6.jpg')";
    setTimeout("changeImg6()", 5000);
}

function changeImg6() {
    document.getElementById("mainImg").style.backgroundImage = "url('images/mainImg/image1.jpg')";
    setTimeout("changeImg1()", 5000);
}

window.onload = changeImg6;