A page can declare several candidates
Modern pages often use srcset or picture to provide alternate image sizes and formats. A browser can select one candidate to render instead of using an image element’s literal src.
<picture>
<source type="image/avif" srcset="photo.avif">
<source type="image/webp" srcset="photo.webp">
<img src="photo.jpg" alt="Example">
</picture>In this example, a browser that supports AVIF can render photo.avif. The JPG is still declared as the image element’s fallback src, but it may not be the file currently displayed.
Optimization can also happen at the same URL
Some image servers choose a response format based on the request. In that case, a URL that looks like a JPG or PNG path can still return WebP or AVIF to a browser. A filename alone does not prove the bytes or response format.
When Save Source Image can help
Save Source Image checks the clicked image’s literal img src after you choose its context-menu command. If that URL is usable and is not a placeholder, it asks Chrome to download it directly. This can help when Chrome rendered a srcset or picture candidate while the page also declares another source in img src.
When it cannot
The extension cannot make a JPG or PNG from an image the page does not expose. If the literal src is WebP or AVIF, is a placeholder, or the server returns WebP or AVIF for that URL, Chrome may still save that format. The extension does not convert or re-encode image bytes.