It’s common to spend so much time trying to get pages to rank that we overlook the images we use on said pages. Sometimes, it’s just as important for a search engine optimization strategy to focus on a single image as it is to rank an entire page. So let’s go back to some SEO fundamentals and review what it takes to rank an image efficiently.

There are three main reasons to rank an image: you want the image to be high on Google (Bing, Yahoo, Etc.) image results, you want the image to lend some juice to the page it’s on, and  they serve as great link bait. So how do you rank them? Here’s a short list of the most important aspects.

-Filename: Your filename should always be relevant, never use an ugly string of numbers and underscores. For instance, SEO_LOGO is a world better than A1210432.

-Alt text: Good alt text should describe what the picture is about as succinctly as possible. You want to include the keyword you’re trying to rank for, but don’t go crazy with it. Just one, relevant keyword in your descriptive alt text will do you fine.

-Surroundings: If you want your image to rank well, surround it with relevant copy. Search engines will look to the writing around an image to get a feel for what the image is about. Basically, if a page ranks well for a term, the relevant image on that page has a good chance to also rank well for that same term.

-File specs: Search engines measure your pages load time, so keep images trim. If anything takes more than a couple seconds to load, it’s probably too big. As a rule of thumb, use GIFs for graphs and charts and JPEGs for pretty much anything else. PNGs  are slightly larger and have traditionally been advised against, but internet speeds are getting to the point where it is almost a non-issue, especially for smaller navigation elements.

Original article about image SEO posted on Wikimotive's blog under the title Image SEO Overview.