Although advances have been made in this area, you should assume that an image to a search engine looks like unreadable code. So what you need to do to surround the image with hints on what the image might be about. This gives you another opportunity to add your primary and secondary keywords to your page.
Before you even upload the image to WordPress consider renaming the image filename from the SEO unfriendly (for example) DCN0019.jpg to a filename that describes the image (such as “wordpress-image-uploader.jpg”). Given how organizationally challenged I am, I don’t understand why people don’t do this, how do you search through images if you leave them with unrecognizable names? When I name an image I avoid spaces as well.
Now you are ready to upload the image into your post. Click on the little box to the right of “Upload/Insert” above your post. When the uploader dialog pop ups, take the few seconds and fill in the tag fields before inserting the image into your post. Here are the tags to fill in.
- alt This tag is the most important. Add a keyword rich description of your image here.
- title Ever notice how a little yellow tag appears on some images when you mouse over them? You can get this effect by setting the title tag. Note that some browsers may not support this well. Is it important for SEO? It depends on who you ask, but I always set it, usually to the same as my alt tag.
- caption Some SEOs feel that captions help the SEO of your images, it’s a nice way to describe the image to your audience as well.
If this really feels like too much of a bother for you, consider installing the SEO friendly images plugin. This plugin will automatically set the tags for you.
Like everything, it’s more powerful if you know how to use it well. The default options assume you have a nice friendly filename that is descriptive of the image. If you are not going to bother with that, then don’t use %name. %title is the post title, which is often a great choice, but keep in mind that if you have multiple images in your post they are going to have the same tags. Still anything reasonably descriptive is better than having blank tags.