This JavaScript checks if all the images in the document exists. If a particular image does not exist, that image will be replaced by a custom image. Works with IE only. In IE, if a particular image does not show up, then its dimensions are 28 x 30 (without the 'alt'). So, the script checks all images with this size after removing the 'alt' tag. If such an image exists, it is a broken-image. The only drawback is that if your image has dimensions of 28 x 30, even if it exists the script will treat it as a broken-image. But there is a solution. You can prevent the script from checking for such scripts by placing an attribute-value pair nc="1".