SEO Beginners - Images as a Signal
When you include an image on a web page, there are a couple of things that you are doing. One of those is to make the page more visually appealing (depending upon the image you are using).
The old cliche that "an image is worth a thousand words" can be true if the image you decide to include actually adds to the page that you've created, and is meaningful. When I talk about images, I often refer to them as "meaningful" images and "non-meaningful" images. When you use little blue arrows on a page as bullet points for list items, chances are that those are non-meaningful images. When the images that you use are purely for decoration, again they don't add much meaning. Both of those can help create emotions or make a viewer feel a certain way about a page, but they don't necessarily help that visitor understand what the content of the page is.
When you have a page about Lions, and you show a picture of a football player dressed in a Detroit Lions uniform, your picture tells us that you're talking about members of the football team. If your picture shows a lion trekking about on four legs, and hunting a meal, the page is about a completely different kind of lion.
Usually a search engine will look at what they refer to as "meta data" to try to understand what the content of a picture might be, which isn't what we often refer to as meta data when talking about web pages. This picture based meta data can include things like the file or picture name for the image, the directory that the picture might be in on a website, alt text associated with the image, a caption that might be used with the image, and the text upon a page where the image exists on the Web.
There may be other things about an image that a search engine might look at when ranking an image in an image search. I wrote about some of them in this post:
How Do Images Get Ranked in Image Search?http://www.seobythesea.com/2008/05/how-do-images-get-ranked-in-image-search/
Likewise, an image on a page might help that page rank better for some particular query as well. If you're creating a page about the Detroit Lions for instance, having a picture of the Stadium they play in, a Lions football helmet, a Lions player, with appropriate file names, captions, and alt text can help that page rank better in search results for the query "Detroit Lions".
A Microsoft patent from a few years ago detailed many of the kinds of things they might look for when using images to help pages rank for certain things, and I wrote about those in:
How Search Engines May Use Images to Rank Web Pageshttp://www.seobythesea.com/2008/09/how-search-engines-may-use-images-to-rank-web-pages/
Some of those factors or signals may surprise you. It's also possible that Google looks at other signal and may ignore some of the ones that Microsoft might look at. I like that we have both, to compare and contrast, though.
There may be a time in the future where Google may not need to look at the meta data I mention, and instead can understand exactly what a picture contains, like in this deep learning experiment that Google conducted, where their computers learned to recognize cats:
Google computer works out how to spot catshttp://www.bbc.co.uk/news/technology-18595351
Yesterday in a Google Hangout, we were discussing Google's Layout algorithm, and how the search engine might segment parts of pages, and identify which parts were advertisements, and I suggested that they might do that by looking at the features that different segments of pages might contain. Here's a post about a Microsoft patent I wrote about where they pointed out a way to do that:
How a Search Engine Might be able to Tell Whether an Image is an Advertisementhttp://www.seobythesea.com/2011/03/how-a-search-engine-might-be-able-to-tell-whether-an-image-is-an-advertisement/
Regardless, adding images to the pages that you create, real meaningful images that are engaging to viewers that can help pages rank better for the topics and words that you want them to rank for adds additional signals to search engines on what a page is about. Choose your images carefully, and the names for those image files, the alt text you use, and captions as well, and you're helping to reinforce in a positive way the other signals that your pages are sending to potential viewers.