Review picture elements that select images by format or display conditions. Check fallback images, alternative text, dimensions, and source ordering, then provide corrected HTML with JPEG or PNG fallbacks for browsers that cannot use the selected formats.
Use when reviewing image assets, markup, and CDN or build transforms related to Use <picture> with an <img> fallback. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.
Review the instructions the agent will receive before you install.
A <picture> without an <img> fallback renders nothing in browsers that don't support <picture> (IE11) or don't support any of the <source> formats. The <img> child is also where alt, width, height, loading, and fetchpriority attributes live—these apply regardless of which source the browser selects.
<picture> must end with an <img> element—it is the required fallback and carries alt<source> elements are evaluated top-to-bottom; the first match winstype="image/avif" and type="image/webp" on <source> for format selection<img src> should point to a JPEG or PNG—the universal fallback for all browsersScan all <picture> elements in this codebase. Verify: 1) Every <picture> has an <img> as its last child (required fallback). 2) The <img> has an alt attribute. 3) The <img> has width and height attributes. 4) <source> elements appear before the <img> child. 5) Each <source> has either a srcset attribute or a media attribute. 6) format-selecting <source> elements have a type attribute (type="image/avif", type="image/webp"). Flag any <picture> missing an <img> child or with <img> not as the last child.
For each <picture> element with issues: 1) If missing <img>: add <img src="{fallback-url}" alt="{description}" width="{w}" height="{h}"> as the last child. 2) If <img> is not last: move it to after all <source> elements. 3) If <source> elements lack type attributes for format selection: add type="image/avif" or type="image/webp". 4) Verify the <img src> points to a universally supported format (JPEG or PNG) as the ultimate fallback. Show the corrected <picture> markup.
Explain how the <picture> element works. Browsers evaluate <source> elements in document order and use the first one whose conditions match (type, media, srcset). The <img> element is the fallback for browsers that don't support <picture> (IE11) or don't support the source format. Without an <img> child, <picture> is invalid HTML and produces no output. The alt attribute must be on the <img>, not the <source> elements—it applies regardless of which source is selected.
Review image assets, markup, and delivery configuration related to Use <picture> with an <img> fallback. Flag exact files or components where format choice, sizing, or loading behavior violates the rule, and describe how to confirm the fix in DevTools.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/images/picture-element
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