Image optimization 101: How to rank higher in image search

SEO is not only about optimizing written content.

The increasing dominance of visual content online has brought with it new opportunities for increasing a site’s search traffic by optimizing videos and images.

Optimizing your images gives your website an additional chance to be found via image search, and a good logo or some eye-catching graphics can be just as effective at attracting visitors to your website as your written content.

But even if you’re highly familiar with optimizing written content for search, you may not know where to begin with optimizing images. What factors do you need to bear in mind? Does keyword usage still apply?

In this guide, we’ll take you through everything you need to know about optimizing for image search.

N.B.: This is an updated version of a guide by Dave Davies that we originally published in 2013: Image Optimization: How to Rank on Image Search

Image size

The size of your images can have a big impact on your overall site speed (which is an important search ranking factor), and big, heavy images are one of the biggest culprits for slowing down websites – particularly on mobile.

However, because you also want your images to look good and be eye-catching, especially if they’re the first part of your website that people see in image search, you also don’t want to sacrifice quality. Thus, finding a balance is necessary.

Matt Owen’s article on how to optimize your page images to increase site speed gives some useful pointers here, particularly with regard to not uploading images which are larger than the user will ever see, as this will just slow down your site with no benefit to you or the user.

Which file types are going to be most helpful here? GIF, JPEG and PNG are the three main image file types, which make up 96% of the Internet’s image traffic.

PNG offers a good combination of compression ratio and image quality, and as such is usually your best bet. JPEG can have a compression rate of up to 10x more than the other two formats, but is a lossy format – meaning that it reduces the quality of your images as it compresses them, so consider whether this is a sacrifice you need to make.

Saving your image as a GIF won’t result in a loss of image quality, but it can sometimes reduce color detail, making GIFs most suited to animated images, logos and any other small, simple images.

Google’s PageSpeed Insights offer some more guidelines on how to optimize your images for maximum site speed. 

Image name

The name of your image file can help search engines discover your content in context. This is where keywords enter the picture (as well as in the alt attributes, which we’ll cover below).

If you’re uploading a photo of nature photography, a relevant filename like nature_photography.png has a better chance of ranking well in search than than DSC_1977.png. If it’s possible to be even more specific, such as Hong-Kong-botanical-gardens.png, then that’s even better for SEO.

If you don’t enter a separate title for your image upon upload, the filename will also serve as the image title, which makes it all the more important to be clear and accurate with your filename.

For more on how to optimize your image title text and alt text, read on to the next section.

Alt attributes

Alt attributes are the text alternatives to your image which will appear if your image fails to load, or if the user is accessing your site with an assistive device such as a screenreader. Because web crawlers don’t have eyes, they’re also what search engines “see” instead of an image, making them important for both accessibility and SEO.

As such, the alt text and title text tag fields are the best place to put any keywords relevant to your image, BUT: do not keyword-stuff! This is a poor practice in image SEO just as in text-based SEO, and will do the screenreader users accessing your website no favors.

Title text

The title text is effectively the name of your image, and as such serves a very similar purpose to your image filename. The main difference is that it needs to be human readable as well as machine readable – so use spaces to separate the words in your image, not underscores or dashes (or nothing at all).

There are certain circumstances in which title text is all you need to substitute for your image – if the title text alone describes the image, you don’t always need alt text.

For example, if the image is a headshot of a person, their name alone is sufficient for title text – as it tells both people and search engines what the image is of – and no additional details are necessary in the alt text. Alt attributes are important, but you don’t need to go overboard!

Alt text

This is the field that describes what your image depicts. Alt text can help search engines work out not just the content of an image but the topic of the surrounding text – so it’s important to get it right.

If possible, at least one image on your page should contain your focus keyword, but it’s important not to shoehorn it in. Image alt text should be clear, descriptive, and written in natural language. Imagine it as if you were telling someone who couldn’t see the image what it was about. Which key details would you highlight?

Some guides will place a recommended length on alt text, such as 80 or 150 characters, but in truth the alt text should be as long as it needs to be in order to get the image content across. Try to be succinct, but don’t sacrifice necessary details for the sake of length.

Here is an example of an article graphic (courtesy of Shutterstock) that we uploaded for a recent article, ‘Beyond Google Analytics: 10 SEO analytics and reporting tools‘. The WordPress backend clearly indicates where to input title and alt text:

A screenshot of an image attachment in WordPress with the title text and alt text fields filled in. The caption and description fields are blank.

The alt text we input for this image is as follows: Image of a person typing on a laptop with paper and pens by the side, and a variety of different analytics icons sketched above it, such as graphs, charts and a clipboard.

Page URL and domain authority

The URL of the page that the images are hosted on can affect the image search traffic. If an image is hosted on an optimized page URL on a page which contains quality and relevant content, your chances of image SEO success will be much higher.

Along with the page URL, the page’s domain authority that also can affect an image’s performance in Google Image Search. If a domain already has a reputation for offering quality and relevant content, your image will do better in search. Image SEO is no different to text-based SEO in this regard.

Surrounding content around images

Image optimization doesn’t happen in a vacuum. As such, the copy that surrounds an image on your page is also important for SEO. The relevance of the content, its quality, and the keywords that are used can all affect how the image ranks in search.

The most important copy is the text that immediately surrounds the image. This might be an introductory sentence which precedes the image (for example, “Below is a graph showing the results of a survey carried out among 500 marketers…”) and/or a caption below it which gives some additional context.

Search engines like Google will use this copy to determine how well the image matches the topic of the page. For example, if the focus of the content is on plumbing, an image of a tree has decreased chances of ranking high for the keyword “plumbing examples” (and is likely to confuse your users to boot).

In addition to this, Google’s image recognition AI has become much more sophisticated in recent years, to the point where it can often identify whether the image subject matches up with the rest of your content.

Stock photography

There has been a long discussion over the years on whether using stock photography has a negative effect on your ranking. Google’s Matt Cutts went on the record back in 2013 to state that stock photos do not harm your search rankings, and therefore there is no difference in using them instead of original photos, SEO-wise.

However, there are a couple of caveats to this. One is that stock images are by their nature generic, and so the visual experience of your website will be a lot more generic as a result, particularly if you use a lot of them. This will also not help your image stand out in search results, and a stock image is unlikely to grab the user’s attention – unless of course you’re a stock photography vendor.

The second thing to bear in mind is that there will be countless other copies of the same image as yours out there on other people’s websites. As Dave Davies pointed out in the 2013 version of this guide, “Google doesn’t want to rank multiple copies of the same image any more than they want to rank multiple copies of the same content. If you’re using the same image that’s been found on a hundred other sites before you, why should yours rank?”

For example, if you’re writing about your company’s business culture, you can either pick a stock photo of happy people in an office environment, or simply upload a high-quality photo of your own office with your team members during a meeting. The latter is personal, relevant and interesting, and gives users a sense of what your company is really like.

Content quality is also important in images as it is in text. Matt Cutts pondered in 2013 whether original images might be used as a future quality signal to indicate a trustworthy website, leading to a higher search ranking:

“Who knows – maybe original image sites might be higher quality, whereas a site that just repeats the same stock photos over and over again might not be nearly as high quality.”

While we don’t have concrete confirmation as to whether Google went on to use this as a quality signal in image search, the impression on the user is worth taking into account.

Image engagement and popularity

Search engines value content with high engagement. This means that if you have a high-quality, relevant and original image that starts becoming popular among users, you have more chances of seeing it higher on search results. As with any text post, the popularity of your content can help it reach higher on the SERPs.

The principles of link-building also apply to image search: the more people link to your image, the higher the chances of increased search traffic coming from it. This can also be facilitated by the use of sharing buttons alongside your images. Once your image gets shared on many sites, its popularity will contribute to its success in search.

The popularity of an image can derive from clicks to your site, embeds and shares on other pages, or even social shares. All of them make the image more popular, while also indicating its relevance to the topic it describes. This ultimately makes search engines pay more attention to it.

Overview

In summary, here’s how you can optimize your images to rank higher in search results:

  • Try to reduce the weight of your images, but not to the detriment of quality
  • Pick a relevant filename
  • Use alt attributes to describe your content as accurately as possible
  • Pay attention to the content that’s surrounding your images
  • Try to use original graphics or photography
  • Aim for engaging images that will encourage sharing

Related reading

Image of a person typing on a laptop with paper and pens by the side, and a variety of different analytics icons sketched above it, such as graphs, charts and a clipboard.

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