afair, this prints dimensions for all background images on the page

gistfile1.js

console.clear && console.clear();
var images = [];
var elements = document.querySelectorAll('#global div');
for (var i = 0, l = elements.length; i < l; i++) {
    var element = elements[i];
    var bgImg = document.defaultView.getComputedStyle(element, null).getPropertyValue('background-image');
    if (bgImg == 'none') {
        continue;
    }
    var match = bgImg.match(/url\((.+)\)/);
    var image = {
        url      : match[1].replace(/\"/g, ''),
        source   : element
    };
    var index = images.push(image) - 1;

    var el = new Image();
    el.src = image.url;
    el.onload = (function(images, index) {
        return function(event) {
            images[index].d = [this.width, this.height].join('×');

            if (images.length - 1 == index) {
                for (var k = 0; k < images.length; k++) {
                    var image = images[k];
                    var slice = image.url.match(/^.+\/(.+)\./)[1];
                    console[(!image.d) ? 'group' : 'groupCollapsed'](image.url);
                    console.log(slice);
                    for (var prop in image) {
                        (prop != 'url') && console.log(image[prop]);
                    }
                    console.groupEnd(image.url);
                }
            }
        }
    })(images, index);
}