Should every image be lazy-loaded?

No. Load above-the-fold images immediately; lazy-load only lower ones.

Is lazy loading bad for SEO?

Standard loading="lazy" or proper implementations are crawlable; avoid relying solely on scroll events.

Image Lazy Loading

⚙️ Engineering & Technology By CampusDown Wiki Editorial Team Last updated October 27, 2026

Image lazy loading is a performance technique that loads only images approaching the screen as users scroll, instead of all images at once.

Contents

1. Why load later
2. Implementation and the first-screen exception
3. Layout shift and placeholders
4. FAQ
5. References

Why load later

Long product lists and articles hold dozens of images; loading all at once delays the first screen and wastes mobile data. Lazy loading fetches images as users approach them. A fast first screen feels fast (Nielsen, 1993; Card et al., 1991), especially with infinite scroll or carousels.

Implementation and the first-screen exception

The simplest approach is loading="lazy" on img tags (web.dev, n.d.-a), or Intersection Observer for finer control (MDN, n.d.). Lazy-loading large above-the-fold images delays them; initial responses matter most (Miller, 1968), so load hero images immediately and prefetch slightly ahead for fast scrolling.

Layout shift and placeholders

Late images pushing text down make users lose their place or mis-tap; web.dev (n.d.-b) measures this as CLS. Set width and height or aspect ratio to reserve space, fill it with blurred previews or skeleton screens, and always provide alt text per WCAG 2.2 (W3C, 2023) 1.1.1.

FAQ

Should every image be lazy-loaded?: No. Load above-the-fold images immediately; lazy-load only lower ones.
Is lazy loading bad for SEO?: Standard loading="lazy" or proper implementations are crawlable; avoid relying solely on scroll events.

Sources reviewed: 2026-10-27

References

web.dev. (n.d.-a). Browser-level image lazy loading for the web. Google. How loading=lazy works.
web.dev. (n.d.-b). Cumulative Layout Shift (CLS). Google. Layout shift metric.
MDN Web Docs. (n.d.). Lazy loading. Mozilla. Lazy loading techniques.
Nielsen, J. (1993, January 1). Response time limits. Nielsen Norman Group. Response time limits.
Card, S. K., Robertson, G. G., & Mackinlay, J. D. (1991). The information visualizer, an information workspace. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (pp. 181–186). ACM. Perceptual time constants.
Miller, R. B. (1968). Response time in man-computer conversational transactions. In Proceedings of the December 9–11, 1968, Fall Joint Computer Conference, Part I (pp. 267–277). ACM. Delay versus expectation.
World Wide Web Consortium. (2023). Web Content Accessibility Guidelines (WCAG) 2.2. Criterion 1.1.1 text alternatives.

Reports and materials that use this theory (Korean)

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This article was last updated on October 27, 2026. It is based on widely recognized original works and textbooks; when citing it in a paper, please check the original sources listed in the references.