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According to this article, it's perfectly valid to use alt="" on purely decorative images. For example, if there is a graph showing some data which is detailed on the the page contents, any alt value other than the empty string would be redundant.

To better visualize this, it's possible to access any website with a command-line browser such as Lynx, where the alt attribute is displayed instead of the original image. Sometimes, the alt just repeats content alredy covered in the page contents, and it's pointless to show something in such enviroments. In those cases, alt="" would prevent anything from being rendered, and the page would actually look better on Lynx.

My question is, a website would suffer any penalty in terms os SEO if alt="" is used on some of it's images, supposing that this is the case only when the alt would be redundant? Or it would be better for ranking to keep every alt, even if redundant? Typically, SEO rules seems to be consistent with the HTML specs and good practices, but this is the case on this situation?

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5 Answers 5

[I'd be careful with that document, by the way. I can't find a definition of "update"(Jan 2012) vs. "revision"(Aug 2002), but either way, there's plenty of information on-line that's known to be up to date versus trying to figure out what's going on there.]

For example, if there is a graph showing some data which is detailed on the the page contents, any alt value other than the empty string would be redundant.

This is not true. Alt text is intended as a replacement for the image it's applied to.
If the image is primarily decorative(a slightly better term), then yes leave the alt blank because it doesn't really convey much "information" to, for example, blind users.

Your example situation is much more case-by-case, but if your text says something like "survey data show an increase over time as in fig. 1" the alt text should be able to replace the image altogether. It should read something like "graph showing increase of [data] from [x value] to [y value] over [timeframe]." so that, for example, a blind reader actually gets value from it. If your text goes over the graph contents in great detail, then maybe you could get away with not doing that. But realistically, screen reader users deal with this all the time, can recognize the duplication, and have tools to skip and so on.

Sometimes, the alt just repeats content alredy covered in the page contents

You're interpreting the situation incorrectly.
Yes, as you describe this, it would probably be better to leave that alt text out. But because that alt text sucks, not because it shouldn't be there at all.
Ideally, what you should do in response to this situation is provide better alt text.

In those cases, alt="" would prevent anything from being rendered, and the page would actually look better on Lynx.

"Looking better" as any sort of consideration for alt text is a sign of missing the point.

[would] a website suffer any penalty in terms os SEO if alt="" is used on some of it's images

Penalty? No. The only possible assumption for empty alt text is that it was left out because unnecessary. It's a neutral situation.

Or it would be better for ranking to keep every alt, even if redundant?

Don't make your alt text redundant, anymore than you would repeat a paragraph of body copy.
Alt text is content even though you usually don't see it.

On the other hand, if you can't commit to creating decent alt text, then sure it would probably be better to just leave it out, rather than, for example automatically sticking the image filename in there, as some applications do.

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Yes, decorative images, thats what I meant. My intention is not to skip every alt attribute. Meaninguful images should really have a good alt text. My point is exactly decorative images, such as the the logo of Pro Webmasters, at the top. Since the "Pro Webmasters" text follow the logo, I believe that it would be better to use alt="" on it, right? (ps.: suppose that this logo was inserted on the HTML, and not via CSS, as is the case). –  Metalcoder May 3 '13 at 19:06
  • If your image is a spacer or purely decorative, use alt=""
    • <img src='blank.png' alt="">
    • <img src='rounded_uppercorner.png' alt="">
    • <img src='horizontal_rule.png' alt="">
  • If your image contains rendered text, use that text as the alt
    • <img src='logo.png' alt="My Company Name">
    • <img src='menu_item_news.png' alt="News">
  • If your image is meant as illustration, describe that image so that somebody using a screen reader can get the same utility from the image, or at least know what they are missing.
    • <img src='kids.png' alt="Two children playing with a ball in the front yard">
    • <img src='engine.gif' alt="Animation of a four cycle engine showing its mechanical properties">

If the text in the alt tag is redundant, than it should omitted, it will frustrate users with screen readers. For SEO purposes, Google picks up keywords for image search from text surrounding images, not just from the alt text. In such a senario, make sure to put any text associated with an image directly above or below the image in the same div (with no other intervening markup): <div><img src="kids.png"> Two children playing with a ball in the front yard</div>

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up vote 1 down vote accepted

I did some research, and given all that I read, everybody seems to agree that the alt text should really be an alternative, and alt="" is perfectly fine. This article suggests alt="" only in case of spacers. I don't agree. If good titles and filenames are used, stuffing alt with repetition looks like a wasted of time, and a completely disregard for accessibility.

So, my conclusion is, there is no problem in using alt="", if the alternate text just repeats everything else. And since it's best for accessibility, it's best to stick to alt="" when that is the best answer. This quote sumarizes everything (emphasis mine):

People often forget that alternative text can be a great place to put search engine keywords. Alternative text is important and required on images, so search engines are unlikely to penalize you for putting keywords there. But remember that your first priority is to your readers. Keyword spamming in alternative text can be detected and search engines change their rules all the time to prevent spammers.

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Who is talking about "spacers" in 2013?! :) –  w3d Jun 14 '13 at 19:31
    
@w3d you never know what you will find in the wild! –  Metalcoder Jun 14 '13 at 20:11

Interesting question. The way I see it, alt text should be redundant. Alt text exists as an alternate to an HTML image - I believe it was originally intended to display in the place of images when the page was for some reason not loading image content.

But since the late 90's, there's a more important use for alt text - accessibility. Screen-readers for the blind read alt text to blind users so that they don't miss the image context when viewing a page.

So by its very nature, alt text should be redundant.

For SEO, Google and others do pay attention to alt text - which is why adding alt text including primary keywords can often positively affect your search rankings. So while you won't suffer a penalty for not having it, you won't gain the benefit, either.

Sounds like your case is a tradeoff - if most of your users use Lynx, you might want to avoid it and go without alt text. But otherwise, in the interest of accessibility and SEO, I would say use it.

(& otherwise, someone needs to get Lynx up to speed on web standards. But that's another conversation.) ;)

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1  
But if the alt is redundant, it would render the content as a verbose (and boring) version. I believe that in this case, it is better to not repeat yourself, from the point of view of a user. But this redundancy would be considered by the Google? By the way, probably none of my users will use Lynx; I just used it to get an idea of how a given site would be perceived by the Google robots. –  Metalcoder May 3 '13 at 17:50

If you want your pictures to be more discoverable on the web, I would recommend you to provide "useful, accurate information in your ALT attributes".

Source: http://googlewebmastercentral.blogspot.co.uk/2007/12/using-alt-attributes-smartly.html

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Having your pictures discoverable isn't necessarily the same as on page SEO. –  w3d Jun 14 '13 at 19:29

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