Why not captions?

Hi Ralf, yes, there are some technical reasons why it’s not worth automatically using image captions as alt text. Human written titles typically make perfect alt text, but human written captions are typically too lengthy for alt text and are already visible on the page – these two effects are both bad for SEO. To elaborate:

* Image alt text is “semi hidden content” and is therefore automatically treated with extra suspicion by search engines when scanning for “keyword stuffing” which is an old fashioned spam tactic. So if images have chunky alt text, especially if the images are small, it can be interpreted by search engines as “keyword stuffing within semi hidden content”, so the site’s rankings could get penalised/lowered in search results.

* Captions are visible on the page beside the image, so for search engines and screenreader-assisted users (the people we make alt text for) the caption appears twice (in place of the image and beside the image) – this is a bad user experience and will be deemed by search engines as minor “duplicate content” which is at worst a spam signal and at best a sign of editorial incompetence so rankings may fall further.

References
These articles don’t go into detail on this particular issue but they do provide context & explanation of the technical SEO terms I’ve used here.

Keyword stuffing: https://support.google.com/webmasters/answer/66358

Hidden text: https://support.google.com/webmasters/answer/66353

Duplicate content: https://support.google.com/webmasters/answer/66359

Things to Avoid > Duplicate content and Keyword Stuffing: https://www.bing.com/webmaster/help/webmaster-guidelines-30fba23a

• This reply was modified 8 years ago by Dan.
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• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.
• This reply was modified 8 years ago by Dan.

Yes, there are some technical reasons why it’s not worth automatically using image captions as alt text. Human written titles typically make perfect alt text, but human written captions are typically too lengthy for alt text and are already visible on the page – these two effects are both bad for SEO. To elaborate:

* Image alt text is “semi hidden content” and is therefore automatically treated with extra suspicion by search engines when scanning for “keyword stuffing” which is an old fashioned spam tactic. So if images have chunky alt text, especially if the images are small, it can be interpreted by search engines as “keyword stuffing within semi hidden content”, so the site’s rankings could get penalised/lowered in search results.

* Captions are visible on the page beside the image, so for search engines and screenreader-assisted users (the people we make alt text for) the caption appears twice (in place of the image and beside the image) – this is a bad user experience and will be deemed by search engines as minor “duplicate content” which is at worst a spam signal and at best a sign of editorial incompetence so rankings may fall further.

References
These articles don’t go into detail on this particular issue but they do provide context & explanation of the technical SEO terms used in this answer.

Keyword stuffing: https://support.google.com/webmasters/answer/66358

Hidden text: https://support.google.com/webmasters/answer/66353

Duplicate content: https://support.google.com/webmasters/answer/66359

Duplicate content & Keyword Stuffing: https://www.bing.com/webmaster/help/webmaster-guidelines-30fba23a