var avatars = document.evaluate('//*[@class="title"]//img', document, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);

for (var i = 0; i < avatars.snapshotLength; i++) {
    var img = avatars.snapshotItem(i),
        imgCan = new Image();
        canvas = document.createElement("canvas"),
        ctx = canvas.getContext("2d"),
        canvasCopy = document.createElement("canvas"),
        ctxCopy = canvasCopy.getContext("2d"),
        scaleFactor = (1 / 3),
        imgHeight = img.height,
        imgWidth = img.width,
        scaledHeight = imgHeight * scaleFactor,
        scaledWidth = imgWidth * scaleFactor;

    imgCan.src = img.src;
    canvas.width = scaledWidth;
    canvas.height = scaledHeight;

    ctx.drawImage(imgCan, 0, 0, scaledWidth, scaledHeight);

    canvasCopy.width = imgWidth;
    canvasCopy.height = imgHeight;
    if(typeof ctxCopy.mozImageSmoothingEnabled != 'undefined')
        ctxCopy.mozImageSmoothingEnabled = false;
    ctxCopy.drawImage(canvas, 0, 0, imgWidth, imgHeight);

    imageData = ctxCopy.getImageData(0, 0, imgWidth, imgHeight);

    for (y=0; y < (imgHeight * imgWidth); y++) {

        inpos = y * 4;
        outpos = inpos;

        r = imageData.data[inpos++];
        g = imageData.data[inpos++];
        b = imageData.data[inpos++];
        a = imageData.data[inpos++];

        g = r + g + b;
        g = g / 3;
        g = Math.round(g);

        imageData.data[outpos++] = 0;
        imageData.data[outpos++] = g;
        imageData.data[outpos++] = 0;
        imageData.data[outpos++] = a;

    }
    ctxCopy.putImageData(imageData, 0, 0);
    ctxCopy.save();

    img.parentNode.insertBefore(canvasCopy, img);
    img.style.display = "none";
}