The uploaded original can produce smaller image variants. A srcset lists available candidates, while sizes helps describe the image's expected display width. The browser chooses a candidate based on those hints and its environment.

This is different from simply setting a large image to width 100 percent with CSS. That CSS can make the layout fit while the visitor still downloads a file much larger than necessary.

1. Choose an image that appears too heavy or blurry and record its page URL.
2. Inspect the Image block's selected resolution and the original dimensions.
3. Use browser developer tools to review the image markup and the actual requested file at different viewport widths.
4. Compare the selected file with the displayed size, including a high-density device where relevant.
5. Review theme or optimisation settings if the browser repeatedly receives an unsuitable candidate.

Keep attachment metadata and derivative files consistent. Manually deleting thumbnails or replacing only the original file can leave markup pointing to missing or outdated candidates.

If a theme introduces new image sizes, regenerate the needed variants through a supported process after a backup. If a CDN rewrites image URLs, verify that every candidate remains reachable and uses the intended production domain.

A plain external image URL, custom HTML or CSS background may not receive the same WordPress-generated responsive markup as an ordinary Media Library image. Evaluate those uses separately rather than assuming all visible images share one delivery path.

If a browser chooses a larger file than expected, check its pixel density and caching before declaring the selection wrong. When requesting help, provide the page, displayed width and actual file requested. That evidence allows a targeted correction to layout hints or generated sizes instead of replacing every image with a full-size original.

• Choosing image sizes and preventing blurry displays
• Regenerating thumbnails after a theme change
• Preparing web images before uploading to WordPress
• Writing useful alternative text for WordPress images

• WordPress responsive image design
• WordPress documentation