LazyLoad
LazyLoad is a lightweight, flexible script that speeds up your website
... responsive images, it optimizes your website for slower connections, and can enable native lazy loading. To display content images on your pages, always use the img tag. This would benefit the SEO and the accessibility of your website. To understand if your images are content or background, ask yourself: “would my website user like to see those images when printing out the page?”. If the answer is “yes”, then your images are content images and you should avoid using background images to display them.