Background images and SEO Info on it

Question

At the moment I have on my website some images which are defined in the CSS file as a background image.

The code looks like this.

The HTML:

<a href="http://domain.com" title="Website Title" class="image"></a>

The CSS:

 .image {
    background: url("../img/deelnemende-organisaties/arcadis.png") no-repeat;
 }

Due to some other CSS3 effects with this background it isn't possible to change the background to a normal <img> tag.

Now I was wondering what is the best way to use background images and keeping the SEO ranking as high as possible.

I saw some solutions as:

• Putting text into the <a> tag and then hiding it with CSS with text-indent: -9999em
• Only put a title attribute on the tag with the text in it
• Placing a transparent in the tag with the same title as your tag
• Leave it as I have in my example and building up a so called Image Sitemap in a XML file

Now I'm not sure what is the best solution and I don't wanna screw my SEO ranking by doing something what they call illegal.

Answer 1

Use alt text on a transparent image and then google might factor in a tiny sub KB spacer-like image and that could have an indexing effect however that is speculation  if you main motot is only to improve the seo text indent adds the text content you would have added if it had been an img and is not currently frowned on by Google's indexing algoritham