# Prioritize critical images (prioritize_critical_images)

Sets fetchpriority=high on the LCP image. The prioritize_critical_images filter: what it does, its risks and the Apache, nginx and IIS directives.

Canonical URL: https://modpagespeed.com/docs/filters/prioritize_critical_images/

- Category: Image
- CoreFilters: No
- OptimizeForBandwidth: No
- Risk: Test first

`prioritize_critical_images` sets `fetchpriority="high"` on the images the critical-images beacon has reported above the fold, so the browser front-loads the fetches that most influence Largest Contentful Paint. It is beacon-driven: the page is instrumented, real browsers report which images render above the fold, and the attribute is applied on subsequent responses. It rewrites attributes only and injects no scripts.

## How it works

Enabling the filter also turns on critical-images beaconing.

The filter is a strict no-op until beacon data is available — with no data it would have to guess, and a wrong guess would prioritize a below-the-fold image at the real LCP image's expense. An author-supplied `fetchpriority` always wins, so hand-tuned markup is left untouched.

This filter is opt-in and is not part of any rewrite level. Enable it by name.

## When to use it

- Not in CoreFilters: it runs only when you enable it by name.
- Risk rating on these docs: **Test first**.

## Risks

- Above-fold detection is data-driven and imperfect. The strict no-op-without-data behavior avoids the worst case, but on unusual layouts the beacon may still flag an image that is not truly the largest one.

- The filter backs off on `Save-Data` requests, AMP documents, and disallowed URLs.

## Configuration

Enable it in the module configuration, at server, virtual-host or location scope:

**Apache**

```apache
ModPagespeedEnableFilters prioritize_critical_images
```

**nginx**

```nginx
pagespeed EnableFilters prioritize_critical_images;
```

**IIS (pagespeed.config)**

```text
pagespeed EnableFilters prioritize_critical_images
```

Scoping, `ForbidFilters` and the thresholds filters read: [Choosing filters](https://modpagespeed.com/docs/filter-selection/).

## Live example

See the before and after, with the source diff: [prioritize_critical_images example](https://modpagespeed.com/examples/prioritize_critical_images/).

## Frequently asked questions

**What does the prioritize_critical_images filter do?**

`prioritize_critical_images` sets `fetchpriority="high"` on the images the critical-images beacon has reported above the fold, so the browser front-loads the fetches that most influence Largest Contentful Paint. It is beacon-driven: the page is instrumented, real browsers report which images render above the fold, and the attribute is applied on subsequent responses. It rewrites attributes only and injects no scripts.

**Is prioritize_critical_images enabled by default?**

No. `prioritize_critical_images` is not in CoreFilters, the default RewriteLevel; it runs only when you enable it by name with `EnableFilters`.

**How do I enable prioritize_critical_images on Apache and nginx?**

Add `ModPagespeedEnableFilters prioritize_critical_images` on Apache or `pagespeed EnableFilters prioritize_critical_images;` on nginx. On IIS, add `pagespeed EnableFilters prioritize_critical_images` to pagespeed.config.

## Related filters

- [`convert_gif_to_png`](https://modpagespeed.com/docs/filters/convert_gif_to_png/): Convert GIF to PNG
- [`convert_jpeg_to_avif`](https://modpagespeed.com/docs/filters/convert_jpeg_to_avif/): Convert JPEG to AVIF
- [`convert_jpeg_to_progressive`](https://modpagespeed.com/docs/filters/convert_jpeg_to_progressive/): Progressive JPEG
- [`convert_jpeg_to_webp`](https://modpagespeed.com/docs/filters/convert_jpeg_to_webp/): Convert JPEG to WebP
- [`convert_png_to_jpeg`](https://modpagespeed.com/docs/filters/convert_png_to_jpeg/): Convert PNG to JPEG
- [`convert_to_avif_animated`](https://modpagespeed.com/docs/filters/convert_to_avif_animated/): Animated AVIF
- [`convert_to_avif_lossless`](https://modpagespeed.com/docs/filters/convert_to_avif_lossless/): Lossless AVIF
- [`convert_to_webp_animated`](https://modpagespeed.com/docs/filters/convert_to_webp_animated/): Animated WebP

This page is drawn from the [prioritize_critical_images entry on Image filters](https://modpagespeed.com/docs/image-filters/#prioritize_critical_images). Every filter in one table: [PageSpeed filters](https://modpagespeed.com/docs/filters/).