Updated: Mar 5, 2019
Images are crucial to ensuring that your content is more accessible, attractive, and engaging to users, but they’re equally important in terms of SEO. First, they give search engines important contextual information. Second, optimised images speed up page loading, which increases user engagement and search engine rankings.
To give your brand the best opportunity to succeed with SEO, you should understand the basics of image optimisation. Image optimisation is the process of creating and delivering high-quality images in the ideal format, size, and resolution to increase user engagement. It also involves accurately labelling images so search engine crawlers can read them and understand page context. According to HTTP Archive, images made up on average 21% of a total web page’s weight as of November 2018.
Because images consume more bytes than any other part of a website, their size and complexity heavily influence site performance. If you reduce the size of images without compromising quality, page load times improve and, subsequently, the experience of website visitors does too.
An Aberdeen Group study shows that a one-second delay in load time equals a 7% drop in conversions, and that around 40% of people abandon a website that takes more than three seconds to load. Improved user experience and interactions with your site have a positive impact on search engine rankings, which further improves customer engagement, conversions, and customer retention. What’s more, when optimised images take up less storage space on your server, site backups will be completed more quickly.
Now, I’ll break down how to optimise your images.
1. Resize your images
Image size and file size are not the same thing. Image size refers to the dimensions of an image (e.g., 1024 by 680 pixels). File size is the amount of space needed to store it on the server (e.g., 350 kilobytes).
Images with higher resolution and larger dimensions (often created with a professional camera) slow your page load times considerably. While they work well for print reproduction, you need to scale down the file size without losing too much quality for them to work well on the web.
TIP: Use this guide to identify the best image sizes for social media platforms.
Pick the right file format
PNG, JPEG, and GIF are all popular. Each has its benefits. I recommend JPEG for images with lots of color and PNG for simple images.
Choose the right compression rate
If you compress an image too much, the file size is small but the image quality is poor. On the other hand, when you use a low compression rate, the image quality is high but the file size is huge.
Ideally, you should experiment with your file types and compression rates to see what works best for each image. Many image-editing tools, including Adobe Photoshop, have a “save for the web” option, which automatically minimises the file size while optimising image quality.
If you don’t have Photoshop, here are some popular tools:
Image optimization tools
WordPress plug-ins for image optimisation
Test optimisation for speed
After you’ve optimized your images, how do you know whether your website page loading times are quick enough? Use one of following tools to test your site speed: WebPageTestPingdomGTmetrixWebWaitGoogle PageSpeed Insights As your website and content change frequently, it’s a good idea to keep checking your stats over time.
2. Optimize image file names
Choosing the right file name is important for your page SEO and for ranking in image search results. Before uploading any image, name the file with relevant, descriptive keywords to get the most SEO power. Include target keywords at the beginning and separate them with hyphens.
Don’t use underscores because search engines don’t recognise them and won’t be able to “see” the words individually. File names should make sense to both search engines and humans. For example, the original name for an image of a woman in a hair salon is “salon234.jpg.” Rename it with a clear and more descriptive title such as “woman-having-a-haircut-in-a-salon.jpg.”
3. Use alt tags
Viewers may understand what a picture is about, but search engine spiders still need clues. Without alternative text, it’s impossible for search engines to accurately index your image content. A good alt tag provides context and helps visually impaired users too.
Even when images aren’t loading because of a glitch, search engines can still read the alternative text to help rank a page. Brand-relevant words can be included here to boost visibility. Just avoid keyword stuffing.
Provide more detail than you included in the file name. While no ideal number of words exists, aim for 10 to 15 to convey something about the image.
4. Optimise the image title
If you use WordPress, the image title is usually taken from the name of the file so you can sometimes leave it as it is. If you don’t use WordPress or the title doesn’t explain the image, rename it with the appropriate keywords in the same way as file names.
5. Include captions
Image captions – the words directly beneath images – may not have a direct impact on SEO, but, unlike file names and alt text, captions are visible on a website page.
For this reason, they can add to the user experience. Most people are drawn to image captions to get a feel for the overall content. Without image captions, your bounce rates could increase, damaging your credibility with search engines.
6. Use unique images
Using stock photos is fine, but they won’t necessarily help your search rankings, as other websites often use the same images. In the same way that unique written content is better for SEO, it’s a good idea to upload unique images whenever possible.
7. Ensure that your text complements the images
The copy on the page can help search engines determine the relevancy of your images. If it doesn’t include enough information to explain an image, add more relevant text, and describe the image if possible.
8. Add image structured data
Adding structured data to your pages helps search engines display your images as rich results. Google Images supports structured data for product images, videos, and recipes.
For example, if you have recipes on your site and you add structured data to your images, Google can add a badge to your image showing that it belongs to a recipe.
Use Google’s Structured Data General Guidelines to learn how to add structured data to your pages within the search engine’s parameters.
9. Use site maps
According to Google, a site map is “a file where you can list the web pages of your site to tell Google and other search engines about the organisation of your site content.” In other words, it’s a file that contains a map of your site’s content.
Site maps are an important part of SEO because they tell search engines about all the pages of your site. To ensure that search engine crawlers notice every image – an infographic, meme, photo, video thumbnail, etc. – include them in your site map.
For these image map entries, include the title, description, URL location, caption, and license information. For video entries, include the title, description, URL location, thumbnail URL, and raw video file URL. If your website is hosted on WordPress, you can use Yoast SEO, which will automatically add your visual content to a site map.
If you’re struggling to get your content noticed, keep these strategies in mind before you upload any image. These image optimisation techniques will improve the likability of your content by both search engines and human users.