The dimension of images brings a whole new problem to search engines and optimisation. There are billions of jpegs, bitmaps, gifs amongst many other images to view on the web, all in need of organisation, but it’s not nearly as simple to do so as it is with websites.
Normal HTML pages have titles, metadata, anchor links and backlinks amongst other factors, all of which influence its subject matter and quality as determined by the Google crawlers. With web pages there is all this hidden data alongside the content of the site which help rank it within the searches; images have nothing like this amount to affect the algorithms.
And so Google have to use an entirely different formula to rank images within their image searches, which take into account a multitude of factors, all of which as SEOs and webmasters we should take into account.
First and foremost is the alt-tag. Obviously it is impossible for the Google crawlers to read an image and work out what it is about – it takes an incredibly complication combination of human eyes and brain to do so for us alone. Instead, they read the “alt-tag”, a caption that will replace the image when it cannot be viewed by a browser or crawler. It is essential for the alt tag to be clear and relevant to the image, without being loaded simply with keywords. It is all too easy for a web editor to label an image “check this out” or “click here” but this is simply useless for the Google crawlers – the tag has to be descriptive and relevant.
Here’s an example of good practice:
Daniel Radcliffe on the Harry Potter Red Carpet
For the image to the left, an alt tag like “Daniel Radcliffe on the red carpet for the new Harry Potter film” is good, but if you try “Daniel Radcliffe in a suit on the new Harry Potter film premiere red carpet” it becomes a bit of a mouthful for the user. Google’s Image Search Product manager Peter Linsley explains: “I would treat it like an image title, and if you think about the title of an HTML page, I would give the same sort of treatment.” Keep it simple and descriptive.
Image Source Tags
Google’s crawlers also read the image source tag, which again should take advantage and be relevant without looking like a university dissertation. Be descriptive and clear in how you name the image - the user won't see this, but the Crawler will!
In addition, Google has to decide what text within the page content might be relevant to the image, so captions, titles and descriptions within the text are very good practice in associating and image with relevant text. So if your entire page is about Daniel Radcliffe on the red carpet for the latest Harry Potter film, your image is far more likely to be ranked by Google.
Image size and image placement can also be important – a large picture above the fold and immediately recognisable to a crawler and user is ideal and most likely to be indexed well in image search. Peter Linsley explains that they try and relate importance of images according to the user experience, that is to say if a page is built towards a user experience that is more likely to be favourably looked upon by the crawlers, as although they do not work in the same way as a web user, they aim to prioritise the same aspects.
If you have an article listing various details about one aspect, for example rating the Harry Potter films one by one, you might have an image related to each one and Google’s crawler will usually be able to differentiate the different parts of the article. If it is a blog post it is advised to have a permalink for each entry though.
Images are the easiest way to bring unique content to your site, not least because you can just take a photo of your office where you are working and it most likely will be new to the web. The increasing accessibility of high grade digital cameras and rising quality of mobile phone cameras mean it only gets easier too. Google loves unique content, so it's never been easier to take advantage!
Perhaps unsurprisingly, Page Rank is also taken into account as the importance of the page wears off on an image – so generally good SEO practices will benefit you in image search in the long term.
For once we're going to give you permission to bear the user in mind ahead of the search engine, not least because the search engines think more like users when it comes to images! Keep the user in mind at all times, don't place an image out of place to try and get it prioritied, if it's in a relevant place then it will do that itself. An image well labelled near relevant text, with good titles both within and outside of the metadata, will be well set to get indexed in Google Image Search.
Image search is a highly valuable way to bring traffic to your site – if you have good unique images on your site and indexed by Google you are far more likely to be clicked through on the tenth page of image search than the tenth page of normal search. Users can flick quickly through image search for the picture they want where they might be less patient in normal search. By taking advantage of this and employing good image practices you are more likely to be able to reap the benefits.