WHY OPTIMISE IMAGES?
There are two important reasons to optimise images for websites (not print media).
- Page load speed is an IMPORTANT search engine ranking signal. The need for speed became more important for SEO because:
- More people are using more expensive mobile data than ever.
- Improving the user experience (UX). We’ve all been frustrated with the gradual loading of a photo dumped from a 25-megapixel camera straight onto a webpage.
HOW TO BEST OPTIMISE IMAGES FOR ISO (Image Search Optimisation)?
There are many ways to optimise images, either before or after adding to your website.
Optimise Images BEFORE Adding to Web Pages
IMAGE PHYSICAL SIZE
Feature/header images might need to be wide to show on big desktop screens. I tend to go for a maximum of 1920 pixels wide images for web page header images.
Think about the average width of mobile phones. There are so many makes and models of mobile devices. For most of my images, I tend to use 767 pixels wide because it’ll fit on most tablets without pixellating and after an Boeing aeroplane model is easy to remember.
IMAGE DATA SIZE
Compressing the DATA size of images before uploading can be done with Tinyjpg, Optimizilla, Kraken, CompressNow, GiftOfSpeed, etc.
Optimising Images AFTER Adding to Web Pages
If you use a good WordPress image optimisation plugin, it will use thumbnails of various preset image sizes, detect the device, (eg table) used for seeing images and then serve up the best size image for the device.
Good WordPress image optimisation plugins will convert jpg formated images and serve them up as highly compressed webp formats.
You can configure image optimisation plugins to either losslessly compress for better quality or lossy compressed images for even more speed and slightly less quality. With me being an SEO practitioner I go for less quality in preference for faster loading images which can account for over half the page load speed time. You can adjust the quality of lossy images.
IMAGE OPTIMISATION TIPS FOR SEO
USE RELEVANT IMAGES
- Your images should be relevant to your web page content.
- Irrelevant images will diminish the quality of your webpage content, thus reducing its SERP ranking.
IMAGES IN SITEMAP
Ensure images are included in your site map to make it easy for search engines to crawl images. If using WordPress try the Google XML Sitemap plugin if you’re not using, for example, the Yoast sitemap.
WHAT IS THE BEST IMAGE FORMAT FOR SEO?
- Choose the best image format for SEO.
- jpg (.JPEG) is best for colour photos or gradients/shading.
- png is better for solid colours and transparency
- I dont’ recommend an animated gif but if you do keep it small and simple. You can get already created gifs or you can create them using Giffy.
- You can’t upload .webp images to your WordPress media library yet.
WHY USE IMAGE ALT TAGS?
Image alt tags started as a description for visually impaired people. 19% of searches on Google returned image/s. If you want your images at an attraction and visitor path to your sales information and or brand then use image alt tags.
Use alt image tags for good SEO and increased accessibility.
Incorporate focus keywords in image alt tags but avoid keyword stuffing.