function image() {
};

image = new image();
number = 0;

// imageArray
image[number++] = "<img src='pix/Bild_1.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_2.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_3.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_4.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_5.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_6.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_7.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_8.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_9.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_10.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_11.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_12.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_13.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_14.jpg' border='0'>"
image[number++] = "<img src='pix/Bild_15.jpg' border='0'>"
// keep adding items here...

increment = Math.floor(Math.random() * number);

document.write(image[increment]);