A French website (www.laboratoire-referencement.fr) very often tests differents attributes for Google, Bing and Yahoo to compare their effectiveness.
Let's see today their results for the alt attribute (the alt is used in images)
Aim of the test
The target of this test is to analyze if it is possible to rank a page on a specified keyword, only by using the alt attribute of an image. This test will be done through Yahoo, Google and Bing.
A keyword (defined as KW) has been put in the alt attribute of an image such as<img src="" alt="KW" />
KW is a KeyWord which doesn't exist on any webpage known by Google, Bing and Yahoo.
NB: KW is not the true word used, it is kept secret in order to redo the test several times.
When we were looking for the keyword KW in theses 3 engines, the answer before the test was:
"No answer found" or No pages contain KW
If, after having indexed the test page containing the word KW in an alt attribute, a search engine, for the same query, gives as a result the test page, we can then come to the conclusion that:
(1) - The Alt attribute alone allows to rank a webpage with a given key sentence
If not, one can conclude that:
(2) - The Alt attribute alone cannot rank a webpage on a given key sentence
If we come to the second conclusion, it doesn't mean that the search engines never analyse the content of the alt attribute.
As a matter of fact, it is possible that:
- A keyword only in the alt attribute is not enough to rank a page on this keyword but brings anyway a bonus.
- This attribute is used to fight spam, over-optimization or duplicate contents.
- The test is not genuine for the word KW doen't exist anywhere else on the page.
The test page is not ranked if we make a query with KW on Yahoo nor Bing.
The test page is ranked with the word KW on Google.
Interesting, isn't it?
We have already given you two tips on how to optimize your images on Google Image Search, here is another one.
Make Your Image folder accessible to search engines
Be sure that your robots.txt file does not limit search engines from accessing your images files. As a matter of fact, this is very important if you want that your images got ranked on Google.
Like this, Google will immediatly know where to find it.
If you are afraid someone could steal your image, then add a copyright on it, but do not protect the whole content of the directory, as you are sure Google will never find you...
One tip (more tips will come later) is to use the "Alt text" and "Title tag"
This is one of the most important part of image optimization and you should write a keyword or a phrase which is accurate and relevant to the image and to your webpage. The "alt text" should be inserted in the code for your image file as well as the title.
For example: <img src="filename.gif" alt="Write your alt text here" title="This is the title of your image"/>
Actually, the alt text will be used by the browser (and therefore by the search engine) to understand the content of your webpage and to know why you used an image.
Also vocal browsers (for disabled people) will read the alt text of your image
Basically, the alt text will be displayed if your image cannot be shown, and the title tag will appear when your mouse comes over the image.