Image SEO

Definition

Image SEO encompasses all the optimisations that make images contribute positively to a page's rankings and performance. Core elements: (1) alt text — a concise description of the image content for screen readers and crawlers; (2) file name — a descriptive slug (`seo-audit-score-chart.png`) rather than a camera default (`IMG_4731.jpg`); (3) image format — WebP or AVIF instead of JPEG/PNG saves 25–50% file size with equivalent quality; (4) image dimensions — serving images at the correct size rather than relying on CSS to scale down; (5) lazy loading — `loading="lazy"` on below-the-fold images to defer loading; (6) srcset and sizes — responsive images that serve appropriately sized versions to different screen widths. For editorial content, images can also rank in Google Image Search and drive discovery traffic.

Why it matters for SEO

Images are often the largest contributors to page weight and LCP (Largest Contentful Paint). An unoptimised hero image can push LCP from 1.5s to 5s, which is the difference between a "Good" and "Poor" Core Web Vitals rating. Missing alt text is both an accessibility failure and a missed keyword signal — crawlers rely entirely on alt text to understand image content. Incorrect `loading="lazy"` on the LCP image (which should load immediately) is a common mistake that dramatically slows perceived page load.

How DeepSEOAnalysis checks this

The audit checks: missing or empty alt text on all `<img>` elements; the `loading` attribute on images (flagging `loading="lazy"` on the LCP element); image file format (PNG/JPEG that could be WebP/AVIF); images served significantly larger than their rendered size (oversized images); missing `width` and `height` attributes that cause CLS (layout shift as images load); and whether the LCP element is an image and whether it is preloaded.

Useful tools and resources

• Full performance + onpage audit