SEO Optimization images is becoming more and more essential in SEO (Search Engine Optimization) for websites. The ALT attribute is really a critical step that is sometimes forgotten. This can be a lost chance of better rankings.
In Google's webmaster guidelines, they advise using alternative text for that images in your web site:
Images:. Use the alt attribute to provide descriptive text. In addition, we recommend using a human-readable caption and descriptive text round the image.
Why would they ask us to do that? The answer is simple, really; search engines like google have a similar problem as blind users. They can't see the images.
Many webmasters and inexperienced or unethical SEOs abuse using this attribute, attempting to stuff it with keywords, hoping to achieve a particular keyword density, which is not as relevant for rankings now since it was previously.
On the other hand, high keyword density can, on some search engines like google, trigger spam filters, which may result in a penalty for your site's ranking. Even without such a penalty, your site's rankings won't take advantage of this tactic.
This method also puts persons who use screen readers in a greater disadvantage. Screen readers are software-based tools that really read aloud the items in what's shown on the screen. In browsing the net, the alt attributes of images are read aloud too.
Imagine hearing a paragraph of text that is followed by repetitions of numerous keywords. The page would be far from accessible, and, to put it mildly, would be found quite annoying.
What exactly is an Alt attribute?
An ALT attribute shouldn't be used as a description or a label for an image, though lots of people use it in that fashion. Though it may appear natural to assume that alternate text is really a label or a description, it is not!
The words used within an image's alt attribute ought to be its text equivalent and convey the same information or serve the same purpose the image would.
The thing is to supply the same functional information that the visual user would see. The alt attribute text should function as a "stand in" in the event that the image is not available. Think about this question: Should you replace the look using the text, would most users get the same basic information, and would it create the same response?
A few examples:
If a search button is really a magnifying glass or binoculars its alt text should be 'search' or 'find' not 'magnifying glass' or 'binoculars'.
If an image is meant to convey the literal contents of the look, a description is suitable.
If it is designed to convey data, then that information is what is appropriate.
If it is designed to convey the use of a function, then your function is what should be used.
Some Alt Attribute Guidelines:
Always add alt attributes to images. Alt is mandatory for accessibility as well as for valid XHTML.
For images that play merely a decorative role in the page, make use of an empty alt (i.e. alt="") or a CSS background image to ensure that reading browsers do not bother users by uttering things like "spacer image".
Keep in mind that it's the function from the image we're trying to convey. For instance; any button images should not range from the word "button" in the alt text. They should emphasize the action performed by the button.
Alt text should be based on context. Exactly the same image in a different context may need drastically different alt text.
Attempt to flow alt text with the rest of the text because that's how it is going to be read with adaptive technologies like screen readers. Someone hearing your page should hardly remember that a graphic image is there.
Please remember that utilizing an alt attribute for each image is needed to satisfy the minimum WAI requirements, that are used since the benchmark for accessibility laws in UK and the rest of Europe. They are also necessary to meet "Section 508" accessibility requirements in the US.
It is important to categorize non-text content into three levels:
Eye-Candy
Mood-Setting
Content and Function
I. Eye-Candy
Eye-Candy are things that serve no purpose other than to create a site visually appealing/attractive and (oftentimes) fulfill the marketing departments. There isn't any content value (though there might be value to some sighted user).
Never alt-ify eye-candy unless there is something there which will boost the usability of the site for someone using a non-visual user agent. Make use of a null alt attribute or background images in CSS for eye-candy.
II. Mood-Setting
This is actually the middle layer of graphics which might serve to set the mood or set the stage as it were. These graphics are not direct content and may 't be considered essential, but they are important in they help frame what's going on.
Attempt to alt-ify the 2nd group as makes sense and is relevant. There might be instances when doing so may be annoying or detrimental to other users. Then try to avoid it.
For instance; Alt text that's identical to adjacent text is unnecessary, and an irritant to screen reader users. I suggest alt="" or background CSS images in such cases. But sometimes, it's important to get this content inside for all users.
Most times it depends on context. The same image in a different context may need drastically different alt text. Obviously, content should always be fully available. The way you go in this case is really a judgment call.
III. Content and Function
This is where the image may be the actual content. Always alt-ify content and functional images. Title and long description attributes can also be so as.
The main reason many authors can't figure out why their alt text isn't working is they don't know why the pictures are there. You need to determined exactly what function an image serves. Think about what it's about the image that's important to the page's intended audience.
Every graphic includes a reason behind standing on that page: since it either enhances the theme/ mood/ atmosphere or it is critical to what are the page is trying to describe. Knowing what the image is perfect for makes alt text easier to write. And exercise writing them definitely helps.
A way to look into the usefulness of alternative text is to imagine reading the page on the phone to someone. An amount you say when encountering a particular image to create the page understandable towards the listener?
Aside from the alt attribute you have a couple more tools available for images.
First, in degree of descriptiveness title is within between alt and longdesc. It adds useful information and may add flavor. The title attribute is optionally rendered by the user agent. Remember they're invisible and never shown as a "tooltip" when focus is received through the keyboard. (So much for device independence). So use the title attribute just for advisory information.
Second, the longdesc attribute points towards the URL of a full description of an image. When the information found in a picture is important towards the concept of the page (i.e. some important content will be lost if the image was removed), an extended description compared to "alt" attribute can reasonably display should be used. It may provide for rich, expressive documentation of the visual image.
It ought to be used when alt and title are insufficient to embody the visual qualities of the image. As Clark [1] states, "A longdesc is really a long description of the image...The aim is by using any length of description essential to impart the details of the graphic.
It wouldn't be remiss to hope that a long description conjures a picture - the image - in the mind's eye, an analogy that holds true even for that totally blind."
Although the alt attribute is mandatory for web accessibility as well as for valid (X)HTML, not all images need alternative text, long descriptions, or titles.
In many cases, you are best just choosing your gut instinct -- if it's not essential to incorporate it, and if you don't have a strong urge to do it, don't include that longdesc.
However, if it's necessary for the whole page to work, then you have to add the alt text (or title or longdesc).
What's necessary and what's not depends a lot about the function of the image and its context on the page.
The same image may need alt text (or title or longdesc) in a single spot, but not in another. If an image provides absolutely no content or functional information alt="" or background CSS images may be appropriate to use. But if the image provides content or adds functional information an alt will be required and maybe a long description will be so as. Oftentimes this type of thing is a judgement call.
Listed below are key stages in optimizing images:
Choose a logical file name that reinforces the keywords. You can use hyphens in the file name to isolate the keyword, but avoid to exceeding two hyphens. Stay away from underscores like a word separator, like for example "brilliant-diamonds.jpg";
Label the file extension. For example, when the image search engine sees a ".jpg" (JPEG) file extension, it's likely to assume the file is really a photo, and if it sees a ".gif" (GIF) file extension, it's going to assume that it is graphic;
Ensure that the text nearby the image that's relevant to that image.
Again, don't lose an excellent chance to help your website together with your images searching engines. Begin using these steps to rank better on all of the engines and drive increased traffic for your site TODAY.
Peter Risdon Says:
May 16, 2011 at 2:40 pm | Reply
The paragraph you quoted from ends with this sentence:
“According to the best-sited stations, the diurnal temperature range in the lower 48 states has no century-scale trend.”
That was a surprise given the tenor of this post: “… maybe this is the end to questions as to whether surface temperature increases actually exist.”
Did you mean that we can now say the answer to that is that surface temperature increases do not exist? Or that, pace Keenan in the WSJ, the data do not contain statistically significant trends?
andyrussell Says:
May 16, 2011 at 2:58 pm | Reply
I don’t think diurnal temperature range is very important. Do you?
What’s more, the “century-scale” bit covers some interesting detail. Before Fall et al., it seems that the only work on diurnal temperature range showed a negative trend from the mid-century to 1980s-ish. What Fall et al. found was that this has increased again since the 1980s. So there’s no “century-scale trend”.
But that tells you very little about mean surface temperature trends.
Mark Says:
May 17, 2011 at 10:45 pm
I have heard it claimed that the reduction in diurnal temperature range over the past few decades provides evidence that GHG increases are responsible for the warming. In that sense, some people think diurnal temperature range is important.
Incidentally, I don’t think Fall et al. were the first to find that DTR has increased since the 1980s. I read a paper that said much the same thing a few years ago.
Sorry for the lack of references to back up these statements. I’m a little too busy at the moment to chase them up.
andyrussell Says:
May 18, 2011 at 8:43 am
Ok, so I’m probably not giving DTR as much significance as it deserves.
My point is that I don’t really care about DTR. I don’t think I know anyone who has a particular interest in DTR. If this paper had been published by anyone else I wouldn’t have looked at it. It’s not very interesting. It’s just another paper on climate observations that fits in with the “consensus view of climate change” or however you want to put it. That’s useful, but not to me or most people.
If, however, the paper had shown what Watts has been saying it would show for quite a while now (i.e. that the postitive temperature trend in the surface station record in the US was an artefact of poor station siting) then that would have been very interesting. To me and to many other people.
But it didn’t.
Ben Says:
May 16, 2011 at 4:49 pm | Reply
So Peter… If the diurnal high and the diurnal low both rise by 1°C, you think this means there has been no warming? After-all, the diurnal range hasn’t changed! Others might draw a different conclusion.
Peter Risdon Says:
May 17, 2011 at 8:26 am | Reply
I understand diurnal range has significance, and the relationship between day and night time temperature ranges is important, especially with regard to the period 1950 to 1980 when the effect of man-made global warming, it has been argued, was masked by a cooling but revealed by the changes in the relationship between these ranges.
I further understand that this argument is based on the idea that human pollution caused this daytime cooling, that it affected the range of day time temperatures as well as the difference between night time temperatures which continued to show warming, and daytime ones that didn’t. This makes day time temperature range significant: if this is right it would be expected to show a variation that correlates with human activity.
But this isn’t my field; I’m just reading what I can in an attempt to understand as much as possible about an important issue and, for me at least, that means reading Watts and reading this blog. Just searching out stuff you’re already disposed to accept isn’t good enough. My comment was prompted by what struck me as a somewhat partial quotation and exasperation: I’m with Feynman when he said you should point out the problems with a theory, not just the things that support it.
[It's not really a "partial quotation" is it? That sentence you are interested in is stuck on the end of the abstract as a new paragraph and isn't really related to the 2 sentences I quote and which are related to the subject of this post. I'm not really interested in DTR and I doubt Watts was either. - AR]
At least Watts invites people with different views to post on his blog and has been at the forefront of attempts to cross the ideological divide, not least with Judith Curry.
Ben, of course you’re right. Andy, a century is an arbitrary scale, of course.
I’d still be interested in your take on statistical significance.
JMurphy Says:
May 17, 2011 at 12:05 pm | Reply
In what way has Watts atempted to cross “the ideological divide” ?
Ben Says:
May 17, 2011 at 3:16 pm | Reply
Peter, I encourage a critical (i.e. thoughtful) reading of Anthony’s blog but my god do you really think he’s “at the forefront of attempts to cross the ideological divide”? Anthony has done more to harden denialist thought than anyone, with the possible exception Marc Morano.
The “different views” he solicits are unthreatening fig-leaves.
andyrussell Says:
May 17, 2011 at 3:24 pm | Reply
I’ve got no problem with most of what Keenan says, although he’s not the first/only person to be saying these things. There’s a JoC paper from 2010 and it was one of the useful points to come out of the UEA email enquiries (i.e. working more with stats people). Not sure where the funding was supposed to come from for these new people though!
I suppose the bigger problem comes down to climate science covering so much stuff – you can’t just look at problems from a stats/dynamics/modelling/chemistry/radiation/whatever perspective for too long before a) not getting very far or b) needing to doing something you’ve not done before.