Images are a critical part of running an effective website, but very little of that has to do with SEO. The reason for that is because Google and the other search engines cannot parse the content of an image. Oh, they’re certainly trying. You can bet that Google is working hard on technology that recognizes the content of images, in a general way. Even so, most blog images are only slightly related to the content at hand, generally through symbols or vague meaning. Learning the literal meaning behind them still leaves Google a long way to go.
All of that leaves it to the website owner to provide Google with any possible information about the images they use. How can you optimize your images for search engines?
There’s a lot to consider with the names and alt descriptions of your images.
For the filename, you want to be as descriptive in plain English as possible. Replace spaces in your filename with -s, and camel-case the filename. Treat image filenames as a space for a tiny little smidge of value. Consider an image of a chain when you write a blog post about link chains:
• Bad Filename: 1993831093848.jpg
• Better Filename: notaliterallinkchain.jpg
• Best Filename: Not-A-Literal-Link-Chain.jpg
If you have several similar images in a post, you should avoid giving them all a similar name with numbers to indicate increments. Instead, twist up the content of the name to make it a little more unique.
As for your image description, or alt text, you need to take advantage of that space. Don’t create something too long, or you’ll drive away interest. Remember that your image alt text often shows up in Google Image Search when a user clicks to see that image. Optimize it with keywords and plain English. Always use an alt description. Letting an image go without a description is wasting a resource.
Image size and image format play a big role in behind the scenes SEO. It all comes down to load times. A modern broadband connection might not show you any visible difference in the load times between a 30kb image and a 100kb image. When it comes to an ecommerce site loading 50 of those images at once, however, the speed change can be very visible.
First of all, never use HTML to dynamically resize an image to display it smaller. This doesn’t decrease your loads at all; the browser still loads the image full size, it just scales it down. Instead, open up an image editing program and optimize the image.
What file format should you choose? Some people prefer jpg, some prefer gif, some prefer png. Avoid using tiffs, bmps or any more esoteric formats. Jpg images are typically going to be the smallest, but they are subject to compression artifacts and a deep loss of quality. PNGs save quality much more easily, but they also maintain higher file sizes. Gifs are great for icons and low-detail images, but for more detail they sacrifice either size or quality. Experiment with file types and see where you can strike the right balance between quality and size.
Many people choose to use stock photos for their blog, mostly because stock images are cheap or free and have very little in the way of royalties attached. The problem with stock images, however, is that they aren’t unique to your blog. If someone runs a search and comes across that image in the image search results, the chances of your blog showing up as one of the results is slim.
On the other hand, buying expensive unique images for your blog is typically going to be a high ongoing cost. You don’t necessarily have the budget for 2-3 images per post, however often you post, on an ongoing basis.
The best balance is to take or create your own images, typically using stock photos or free creative commons photos. You can run creative commons searches through Google, Flickr and other image hosts. You can then take multiple images and combine them in unique ways. For this reason, it’s a good idea to have a graphic designer on your staff.
Surprisingly few websites online make good use of captions. One site that does is Cracked.com. Check out any of their list articles and look at the images they use throughout. They always have a funny caption, along with attribution for the image, since they don’t work to create their own or source free creative commons images.
Think of a creative, short sentence that adds a bit of humor or context to your images. Every image has a way you can integrate it with your blog article; if it didn’t fit, you wouldn’t be using it. This is particularly useful for images that don’t quite fit with your topic without a bit of a logical leap. If you can include some kind of joke to help your content along, your readers will appreciate it and it adds that much more value to your page.
Different images have different purposes on your site. Optimize them for that purpose.
Logo and Site Icons. These images don’t need much for alt text and their filenames should be simple. A brand name is all the keyword you need for a logo, and navigation buttons should be simple and descriptive.
Decorative Images. These have the most opportunity for caption, description and filename optimization. Use your keywords and tie in detail as much as possible. See the Cracked.com example.
Infographics. Infographics are typically centerpieces and as such don’t need captions, because the blog post itself acts as a caption. Alt text can be useful, but the image needs to stand on its own for embedding. Filename should be branded and descriptive of the title.
Product Images. Product thumbnails need to be clear and showing enough detail to illustrate the item. Full size pictures should be optimized and high quality, because users use them to judge the quality of the product.
Advertising and CTAs. These typically don’t need captions and the filenames aren’t as important. However, they need to be optimize for quality and color, with plenty of testing.