Element “img” is missing required attribute “src”.

The HTML specification mandates src on the <img> element because an image without a source has nothing to render. Omitting it produces invalid markup and unpredictable browser behavior — some browsers display a broken image icon, while others render nothing at all.

This issue commonly occurs in a few scenarios:

• Templating placeholders — A developer adds an <img> tag intending to populate the src dynamically but forgets to set a default value.
• Lazy loading implementations — Some lazy-loading scripts store the real URL in a data-src attribute and omit src entirely, which results in invalid HTML.
• Incomplete markup — The attribute is simply forgotten during development.

How to fix it

1. Add a src attribute with a valid URL pointing to your image.
2. If you're using lazy loading and want to defer the actual image source, set src to a lightweight placeholder (such as a tiny transparent image or a low-quality preview) and use the native loading="lazy" attribute instead of removing src.

Examples

❌ Missing src attribute

<img alt="A sunset over the ocean">

This triggers the validation error because src is absent.

❌ Source stored only in a data- attribute

<img data-src="/images/photo.jpg" alt="A sunset over the ocean">

While data-src is a valid custom data attribute, it does not satisfy the requirement for src. The validator will still report the error.

✅ Correct usage with src

<img src="/images/photo.jpg" alt="A sunset over the ocean">

✅ Lazy loading with a placeholder src

<img
  src="/images/photo-placeholder.jpg"
  data-src="/images/photo-full.jpg"
  alt="A sunset over the ocean"
  loading="lazy">

Here, src points to a small placeholder image so the markup stays valid, while data-src holds the full-resolution URL for your lazy-loading script to swap in.

✅ Native lazy loading (no JavaScript needed)

<img src="/images/photo.jpg" alt="A sunset over the ocean" loading="lazy">

Modern browsers support the loading="lazy" attribute natively, so you can keep a valid src and still defer off-screen images without any custom scripting.

Learn more:

MDN Reference

HTML img element - MDN

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WHATWG Spec

HTML specification - Embedded content

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web.dev Article

Learn HTML: Images

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