See Crusty Sea: Alt Attribute & SEO Optimization

SEO Optimization images is becoming more and more important in SEO (Seo optimization) for websites. The ALT attribute is a critical step that is often overlooked. This is often a lost chance of better rankings.

In Google's webmaster guidelines, they advise the use of alternative text for that images on your site:

Images:. Make use of the alt attribute to provide descriptive text. Additionally, we recommend utilizing a human-readable caption and descriptive text around the image.

Why would they ask us to achieve that? The answer is simple, really; search engines have the same problem as blind users. They cannot begin to see the images.

Many webmasters and inexperienced or unethical SEOs abuse using this attribute, attempting to stuff it with keywords, looking to achieve a particular keyword density, which isn't as relevant for rankings now since it was previously.

On the contrary, high keyword density can, on some search engines like google, trigger spam filters, which may create a penalty for the site's ranking. Even without this type of penalty, your site's rankings will not benefit from this plan.
This process also puts persons who use screen readers at a greater disadvantage. Screen readers are software-based tools that actually read aloud the items in what is shown on the screen. In browsing the net, the alt features of images are read aloud as well.

Imagine hearing a paragraph of text that is followed by repetitions of many keywords. The page would be not even close to accessible, and, to put it mildly, will be found quite annoying.
What is an Alt attribute?

An ALT attribute should not be used as a description or perhaps a label to have an image, though lots of people use it for the reason that fashion. Although it may appear natural to assume that alternate text is really a label or a description, it is not!

What used within an image's alt attribute ought to be its text equivalent and convey the same information or serve the same purpose that the image would.

The goal would be to provide the same functional information that a visual user would see. The alt attribute text should function as a "stand in" in the event that the image is unavailable. Think about this question: Should you replace the image using the text, would most users get the same basic information, and wouldn't it create the same response?
A few examples:

Some SEO Optimization Tips

If a search button is a magnifying glass or binoculars its alt text ought to be 'search' or 'find' not 'magnifying glass' or 'binoculars'.

If an image is meant to convey the literal items in the image, a description is appropriate.

If it's meant to convey data, then that data is what is appropriate.

If it's meant to convey the use of a function, then your function itself is what should be used.

Some Alt Attribute Guidelines:

Always add alt attributes to images. Alt is mandatory for accessibility and for valid XHTML.

For images that play only a decorative role within the page, use an empty alt (i.e. alt="") or perhaps a CSS background image so that reading browsers don't bother users by uttering such things as "spacer image".

Keep in mind that it's the function of the image we're trying to convey. For example; any button images shouldn't range from the word "button" within the alt text. They should emphasize the action performed by the button.

Alt text ought to be based on context. Exactly the same image in a different context may need drastically different alt text.

Try to flow alt text with the remainder from the text because that's how it will be read with adaptive technologies like screen readers. Someone hearing your page should hardly remember that a graphic image can there be.
Please remember that utilizing an alt attribute for each image is needed to satisfy the minimum WAI requirements, which are used as the benchmark for accessibility laws in UK and the remainder of Europe. They are also required to meet "Section 508" accessibility requirements in the US.

It is useful 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 apart from to make a site visually appealing/attractive and (in many cases) fulfill the marketing departments. There isn't any content value (though there may be value to some sighted user).

Never alt-ify eye-candy unless there is something there which will boost the usability from the site for somebody utilizing a non-visual user agent. Use a null alt attribute or background images in CSS for eye-candy.

II. Mood-Setting

This is the middle layer of graphics which may serve to set the mood or set happens as it were. These graphics are not direct content and may not be considered essential, but they're essential in that they help frame what is going on.

Attempt to alt-ify the 2nd group as makes sense and it is relevant. There may be instances when doing this may be annoying or detrimental with other users. Then try to avoid it.

For instance; Alt text that's identical to adjacent text is unnecessary, as well as an irritant to screen reader users. I recommend alt="" or background CSS images in such cases. But sometimes, it's vital that you understand this content inside for those users.

Most times it depends on context. The same image inside a different context may need drastically different alt text. Obviously, content ought to always be fully available. The way you use this case is really a judgment call.

III. Content and Function

This is when the look is the actual content. Always alt-ify content and functional images. Title and long description attributes may also be so as.
The main reason many authors can't understand why their alt text isn't working is they don't know why the pictures are there. You have to figured out exactly what function a picture serves. Think about what it's about the image that's important to the page's intended audience.

Every graphic includes a reason for being on that page: since it either improves the theme/ mood/ atmosphere or it is advisable to what the page is trying to describe. Understanding what the look is perfect for makes alt text easier to write. And practice writing them definitely helps.
A way to check the usefulness of alternative text would be to imagine reading the page on the phone to someone. An amount you say when encountering a specific image to make the page understandable to the listener?

Aside from the alt attribute you've got a couple more tools available for images.
First, in degree of descriptiveness title is within between alt and longdesc. It adds useful information and can add flavor. The title attribute is optionally rendered through 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 Link to a full description of an image. When the information found in an image is important to the meaning of the page (i.e. some important content will be lost when the image was removed), an extended description compared to "alt" attribute can reasonably display should be used. It can offer rich, expressive documentation of the visual image.

It ought to be used when alt and title are insufficient to embody the visual qualities of an image. As Clark [1] states, "A longdesc is really a long description of an image...The aim is by using any length of description necessary to impart the details from the graphic.

It wouldn't be remiss to hope that a long description conjures a picture - the look - within the mind's eye, an analogy that holds true even for the totally blind."

Although the alt attribute is mandatory for web accessibility and for valid (X)HTML, not every images need alternative text, long descriptions, or titles.

Oftentimes, you're best just choosing your gut instinct -- if it's not essential to incorporate it, and when you don't possess a strong urge to do it, don't include that longdesc.

However, if it's essential 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 on the function of your image and it is context on the page.

Exactly the same image may need alt text (or title or longdesc) in a single spot, but not in another. If the image provides simply no content or functional information alt="" or background CSS images may be appropriate to use. However, if the image provides content or adds functional information an alt would be required and maybe even a long description will be in order. In many cases this type of thing is a judgement call.