Use <img srcset> when an image keeps the same composition and the browser should choose a suitable resolution. Use <picture> when you need to change the crop or composition for a display condition, or offer alternate file formats. In either case, keep an <img> element for the semantic image, alternative text and fallback.
Choose between <picture> and srcset
| Need | Use | Why |
|---|---|---|
| Same image composition, different source resolutions | <img srcset> with width candidates and sizes |
The browser can select a candidate that suits the expected rendered slot and display density. |
| Different crop or composition under a condition, such as a narrow viewport | <picture> with a media-conditioned <source> |
The browser can choose an art-directed image for that condition. |
| Alternative file formats | <picture> with typed <source> elements and an <img> fallback |
The browser can skip a format it does not support and consider the next source. |
MDN describes <picture> as containing zero or more <source> elements and one <img> to offer alternatives for different display or device scenarios: MDN: The Picture element.
Use srcset for resolution switching
When each file shows the same scene with the same crop, provide width-based candidates on the <img>. The sizes attribute describes the image’s expected rendered slot width, allowing the browser to select a suitable source candidate.
<img
src="landscape-800.jpg"
srcset="landscape-480.jpg 480w,
landscape-800.jpg 800w,
landscape-1200.jpg 1200w"
sizes="(max-width: 600px) 100vw,
800px"
width="1200"
height="800"
alt="A kayaker crossing a lake at sunrise">The 800px slot and 600px breakpoint here are illustrative, not universal values. Replace them with the widths your CSS layout actually produces. If the image occupies half a content column, for example, a sizes value that claims it fills the viewport may lead the browser to fetch a larger candidate than necessary.
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How to write a width-based candidate list
- Use a width descriptor such as
480wto state each candidate’s intrinsic width in pixels. - With width descriptors, provide
sizesto describe the rendered slot. It is not the physical width of the source file. - Use realistic media-conditioned slot sizes followed by an unconditional size, such as
800pxin the example. - Do not mix width descriptors such as
800wand density descriptors such as2xin the samesrcsetlist.
When density descriptors are simpler
If the rendered dimensions are fixed and you only need variants for different pixel densities, density descriptors such as 1x and 2x can be more direct. Do not treat sizes as controlling those density candidates; sizes is relevant to width-descriptor selection.
Use <picture> for art direction
Art direction means supplying a different composition or crop for a condition, rather than merely a differently sized copy of the same image. Put the intended media condition on a <source>, then keep the default image in the final <img>.
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<picture>
<source
media="(max-width: 600px)"
srcset="portrait-crop.jpg">
<img
src="wide-landscape.jpg"
width="1200"
height="800"
alt="A kayaker crossing a lake at sunrise">
</picture>The browser checks sources and uses the first suitable one. Put a more specific intended condition before a broader or default source. The <img> must remain last: it is the fallback and the element that carries the image’s alternative text and dimensions. Choose the alt text for the image’s purpose, not to describe the mechanics of the source switch.
Offer alternate image formats with a fallback
For the same visual content encoded in several formats, list typed sources in the order you want the browser to consider them, then provide a broadly usable fallback in <img>.
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<picture>
<source srcset="scene.avif" type="image/avif">
<source srcset="scene.webp" type="image/webp">
<img src="scene.jpg" width="1200" height="800" alt="A kayaker crossing a lake at sunrise">
</picture>A browser can skip a source whose declared type it does not support and consider later sources before falling back to the image. Verify that each file’s actual encoding and the server’s MIME type match the declared format. Do not assume every browser or deployment handles every format identically.
Keep the image meaningful and reserve its space
The <img> remains the semantic image whether or not a <picture> source is selected. Write meaningful alt text when the image conveys information; for a decorative image, use the appropriate empty alternative text. Set intrinsic width and height when appropriate so the browser can reserve the image’s layout space while it loads. The dimensions describe the fallback image; ensure the art-directed alternatives have compatible proportions or account for the layout change in CSS.
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Validate candidates and troubleshoot common problems
- Check the assets. Confirm that each candidate exists, has the expected intrinsic dimensions and contains the intended crop or format.
- Check the real layout. Compare the rendered slot width at the page’s actual CSS breakpoints with each media condition and the
sizesexpression. - Check selection and fallback. Test the conditions you support and verify that the final
<img>loads and its alternative text remains appropriate. - Check format declarations. Confirm that the file encoding and response MIME type agree with each source’s
typevalue.
| Symptom | Likely cause | What to fix |
|---|---|---|
| The browser downloads a source that is larger than the displayed image needs | sizes overstates the slot width, or does not match the real layout |
Describe the image’s actual rendered width across breakpoints, then verify the expression against CSS. |
| A narrow-screen crop never appears | The media condition does not match the viewport, the source URL is wrong, or an earlier source matches first | Test the condition at the intended breakpoint, check the asset URL, and order specific conditions before broad ones. |
| An alternate format is skipped or fails to load | The declared type, actual file encoding or server MIME type is incorrect | Make the declaration and file agree, check the server response, and retain a working <img> fallback. |
| No fallback image or alternative text is available | The required <img> child was omitted |
Add the final <img> and give it the appropriate src, dimensions and alt. |
| Responsive files are not being selected as expected | Width and density descriptors are mixed, or sizes is being used with density candidates as though it controls them |
Use one descriptor type per list; pair width candidates with accurate sizes, or use density descriptors for fixed rendered dimensions. |
Performance and reliability considerations
Responsive candidates can help the browser avoid downloading a source larger than the layout needs, but the actual bandwidth or load-time effect depends on the assets, rendered slot, network and browser selection. Correct markup cannot compensate for missing files, inaccurate dimensions or a misleading sizes value. Check candidate dimensions, test conditions at the real layout breakpoints, and verify fallback behavior rather than assuming a universal file-size or speed improvement.
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Frequently Asked Questions
Can a page use both srcset and <picture>?
Yes. A <picture> can provide conditional or format-specific sources while its final <img> uses srcset and sizes for resolution candidates where appropriate.
Does <picture> replace the need for alt?
No. Put alternative text on the child <img>; it remains the semantic image regardless of which source is selected.
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