Keeping image filesizes as small as possible is very important for SEO. Not only is the loading speed of Pages (also called Page speed) used in ranking Websites by Google but many reputable studies have shown how longer loading times result in fewer sales and more exits from the Page. In short, people get frustrated by slow loading Pages and therefore Google measures the speed of Pages and ranks accordingly. Best practice dictates that every image used on a Website should be tweaked to have it’s filesize reduced.
One means of reducing the filesize of an image is through compression. Compression in the form of zipping an image won’t make any difference to the filesize. This is where lossy and lossless image compression comes in; lossy compression results in a smaller filesize but quality is affected. With lossless compression, image quality is usually unaffected as far as the human eye can see. The best options for Websites is therefore lossless compression.
There are various free Online lossless compression tools such as Yahoo! Smush.it and PunyPNG. If you prefer downloaded applications then PNGGauntlet and Trimage are good. For WordPress there is a very good Plugin called WP Smush.it which I highly recommend.
Choosing the correct image filetype
One of the biggest mistakes people tend to make when creating images for Websites is saving all images in one filetype such as JPG. Right now the three most common image formats used on Websites are JPG, PNG and GIF. PNG and GIF are best for illustrations, line art and icons whereas JPG is best for photographs. PNG and GIF allow for transparency whereas JPG doesn’t.
Saving an image in the ‘wrong’ filetype will usually result in a larger than necessary filesize and substandard image quality. I wrote a post a while back describing the differences between JPG, PNG and GIF.
Image meta matters … alot
Image is just so important, not only for SEO but also accessibility reasons. The Australian government (as well as many other governments) stipulate meeting various accessibility guidelines for Websites such as the Web Content Accessibility Guidelines (WCAG) version 2. For a person using a screen-reader an image is described by underlying meta. Here then are a few SEO and accessibility guidelines for images on your Website:
- File name: Use a descriptive filename. Most cameras for example will name an image something like 8236601.jpg. Rename the image to be descriptive of the content of the image for example house in west pymble.jpg
- Title: The title is what appears when someone hovers over the image so use another descriptive term (if you do this then Google may even include your image in Google Image search results).
- Alternate text: Although this isn’t usually seen, unless the link to your image is broken, this is a critical area in that screen readers read the Alt text as do Search Bots. Remember to include a full-stop/period at the end of the Alt text.
- Caption: WordPress and several other awesome Web software include the ability to add a caption to an image. This is yet another opportunity to describe the image (try not to repeat the Alt text or Title but create an alternate description).
As can be seen from this article there is alot to image SEO (there is alot more than described above). Contact me if you’d like help with your WordPress SEO.