Linked images in galleries aren't replaced

[ms-studio]

Modern Image Formats Plugin doesn't replace linked images in galleries

I just tested the Modern Image Formats plugin. It appears to work fine for single image blocks, and for galleries where the images aren't linked (link set to: none). In those cases, original images (png) are replaced by AVIF files.

However, when the image link is set to "Link images to media files" or "Enlarge on click", then the AVIF is used inside the <img> tag, but the <a href> link (to the bigger image format) is still linking to the PNG version.

Those large images would benefit the most from the size reduction of modern formats. Therefore I consider the plugin's feature isn't complete it those images aren't replaced as well.

Steps to reproduce

1. Create a Post with an Image Gallery, and add some images.
2. Click on the link tool and set "Link images to media files"
3. On the page preview, inspect the source code.

Additional Context

• Plugin Version: 2.6.1

[adamsilverstein]

Thanks for the bug report @ms-studio. Sounds like WordPress is linking to the original files (which might be expected?) however I wasn't able to reproduce this so far with my local and WebP output.

Can you confirm if you changed the default settings under Settings->Media? Do you have the "Output fallback images" option enabled? and the remaining settings (Generate all fallback image sizes, Picture element). Also, are your images large enough to result in a "-scaled" version of the images?

I assume since you mention using AVIF output that your server supports AVIF, can you add your media handling info from Tools->Site Health->Info->Media

[adamsilverstein]

I was still not able to reproduce this with a server that supports AVIF, default settings.

Perhaps this is due to your PNGs, do you know if they use transparency? can you share a few sample images here? do you see the same issue when you test with jpeg uploads?

[ms-studio]

After some testing / investigating, I figured out that the problem appears only when the option "Output fallback images > Also generate fallback images in the original upload format" is checked. Maybe I misunderstood what that setting would do – I assumed that the fallback images would be reserved for legacy browsers.

When inserting those images in a gallery, I find some further strange behavior.

Gallery where images aren't linked

I did some more testing with a gallery where images aren't linked, and the Resolution setting is "Large":

I find that in this case, images encoded to AVIF are served both in AVIF and fallback format, while images encoded to WebP are showing only the fallback versions.

Another observation: I notice that for images encoded from JPEG or PNG to AVIF, sometimes an AVIF format is skipped. For instance this:

The 768x476 size was only generated as JPEG, not as AVIF. The resulting image scrset code in the gallery uses the JPEG for the 768w size:

<img loading="lazy" decoding="async" width="960" height="595" data-id="1225" 
src="https://designbriefs.ch/files/2026/02/ExempelToAVIF-jpg.avif" 
alt="" class="wp-image-1225" style="aspect-ratio:1" 
srcset="https://designbriefs.ch/files/2026/02/ExempelToAVIF-jpg.avif 960w, 
https://designbriefs.ch/files/2026/02/ExempelToAVIF-300x186-jpg.avif 300w, 
https://designbriefs.ch/files/2026/02/ExempelToAVIF-768x476.jpg 768w" 
sizes="auto, (max-width: 960px) 100vw, 960px">

I will try to do some further test in another environment.

[b1ink0]

@ms-studio Could you take a look at this comment if you are encountering this issue?

#1836 (comment)

Most likely, the AVIF images are missing because they were discarded for being larger than their JPG counterparts, which is the default behavior of the Modern Image Formats plugin.

If you want to always use AVIF images in the frontend, regardless of their size, you can use the webp_uploads_discard_larger_generated_images filter. Returning false from this filter will prevent the AVIF files from being deleted even if they are larger than the JPG versions, ensuring that only AVIF images appear in the srcset.

Sample snippet:

add_filter( 'webp_uploads_discard_larger_generated_images', '__return_false' );

[ms-studio]

@b1ink0 Thanks for reminding me :)

I just did some new tests on a clean Local install, with only the Modern Image Formats plugin active.

I activated the setting "Also generate fallback images in the original upload format".

What works

1. After uploading a bunch of PNG images of various sizes, I check the uploads folder: all AVIF images are correctly generated.
2. Using the single Image block, embedding images as thumbnail, medium, full size: this works fine. When embedding the images, it always shows the AVIF format, not the PNG format. Even the full size.
3. Embedding images with a Gallery block, unlinked: this works fine, all images are embedded as AVIF.

The issue

I now change the setting of the Gallery block, and set the link setting to Link to image file.

Expected result: the link should point to the generated AVIF version of the full image size (which does exist in the uploads folder).

Actual result: all links in the gallery point to the full size PNG versions.

I tried various images, PNG and JPG, big and small. The behaviour is the same: all <a href> links in galleries link to the original file.

When the "Also generate fallback images in the original upload format" checkbox is off.

This solves the problem, now galleries link to the AVIF file.

The behavior is the same when the Image output format is WEBP rather than AVIF.

What I'm wondering about:

It's not very clear to me what the checkbox "Also generate fallback images in the original upload format" is supposed to do on the frontend. What I observe when it's active:

• all the <img> tags on the page are using the optimized AVIF/WEBP formats
• the <a href> tag uses the original PNG/JPEG format.

Maybe that's intended? My personal solution is to avoid using "Also generate fallback images..." setting.

[ms-studio]

PS, I just did a test on WordPress playground. I am using this very tiny image as example.

modern-image-format-issue.mp4

[b1ink0]

It's not very clear to me what the checkbox "Also generate fallback images in the original upload format" is supposed to do on the frontend. What I observe when it's active:

There are several reasons why this option exists.

First, when this setting is enabled, if the generated modern image format is larger than the original image, the plugin will serve the original image instead and delete the modern-format version. I think the goal was to avoid degrading performance by serving larger files simply because they are in a newer format.

There is also another related option called Use <picture> Element (experimental). This adds sources for both the modern image formats and the original format inside a <picture> element. If a browser does not support the newer formats, it will fall back to the original image format.

the <a href> tag uses the original PNG/JPEG format.

I don't think it was intentional. My assumption is that if an author links directly to a file, they expect users to receive the original file.

That said, this only makes sense if "Also generate fallback images in the original upload format" is enabled. Otherwise, the link would have to point to the modern image format, as there would be no original-format fallback available.

@adamsilverstein, what do you think? Should file links point to the modern image format as well, even when "Also generate fallback images in the original upload format" is enabled?

cc: @ms-studio