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The deprecated property longdesc on img elements was used in HTML4 to specify the URL of a text or HTML file which contained a long-form description of the image. This could be used to provide optional added details beyond the short description provided in the title or alt attributes.
Here’s an example from HTML4:
<img
src="cat.jpg"
alt="Smiling Cat"
longdesc="image-descriptions/smiling-cat.html" />This, however, is no longer valid in HTML5 and can be converted to the following instead:
<a href="image-descriptions/smiling-cat.html">
<img src="cat.jpg" alt="Smiling Cat" />
</a>Learn more:
Related W3C validator issues
<img> tags, used to include images on a document, require an alt attribute to describe the contents of the image. This is essential for users that cannot see the image (like screen reader users), or as an alternate text when the image cannot be displayed. Example:
<img src="photo.jpg" alt="Person holding a cat" />When an img element has an empty alt attribute, its role is implicitly decorative, so it must not specify a role attribute.
A start tag for <img> has been found inside a <noscript> section within the <head>, where it’s not allowed. Consider moving it to the <body> section.
The HTML <noscript> element defines a section of HTML to be inserted if a script type on the page is unsupported or if scripting is currently turned off in the browser.
When JavaScript is disabled, the content inside <noscript> will be used instead, so this content must fit within its parent section. As an <img> tag is not allowed inside <head>, this will raise an issue. Instead, consider moving the <noscript> part to the <body> section.
This issue is often related to 3rd party tracking pixels like the Facebook or LinkedIn conversion tracking pixels. For example, the Facebook pixel instructions tell you to insert it like this:
<html>
<head>
<script>
...some script...
</script>
<noscript>
<img src="..." />
</noscript>
</head>
<body>
...
</body>
</html>Instead, consider moving the <noscript> part inside the <body>, where the <img> makes sense to be inserted:
<html>
<head>
<script>
...some script...
</script>
</head>
<body>
...
<noscript>
<img src="..." />
</noscript>
</body>
</html>The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
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The src attribute for <img> tags is required, to define the source of the image, like in this example:
<img src="photo.jpg" alt="wombat" />The attributes width and height of <img> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
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The projection media type was deprecated in Media Queries 4.
Media types describe the general category of a device, for example screen, print and speech.
CSS 2.1 and Media Queries 3 defined several additional media types (tty, tv, projection, handheld, braille, embossed, and aural), but they were deprecated in Media Queries 4 and shouldn’t be used.
The src attribute on an element <img> contains a { curly bracket character, which is not allowed unless properly encoded.
Space characters are not allowed in src attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:
<img src="https://example.com/?s=some term" alt="description" />
<img src="https://example.com/?s=some%20term" alt="description" />The src attribute on an element <img> contains a character that is not allowed, and should be encoded.
Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.
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