Most websites are sitting on the easiest SEO wins they will ever get, and those wins are hiding in the media library. Image SEO is the work of making your images fast, descriptive and understandable to search engines, and it is one of the few areas where an afternoon of effort produces a measurable result. Pages load faster, Google Images starts sending traffic, accessibility improves, and every product and service page gets a small but real lift. This checklist covers the whole job: alt text, file names, formats, compression and the technical details most sites never touch.
Why image SEO is the quick win most sites skip
Search engines cannot look at a photo the way a person does. They rely on the signals around it: the name of the file, the alt attribute, the caption, the surrounding copy and how quickly the file loads. Image SEO is simply the habit of getting those signals right, and because most sites never bother, the bar is low. When we audit new clients, images are usually the single biggest source of easy fixes: multi-megabyte photos, camera default names, and empty alt attributes across entire galleries.
The payoff shows up in three places. Rankings, because well-described images strengthen the on-page SEO of the page they sit on. Traffic, because Google Images is a genuine discovery channel for products, portfolios, recipes and anything visual. And conversions, because oversized images are one of the most common reasons a page loads slowly and fails Core Web Vitals.
Alt text: the highest-return five minutes in image SEO
Alt text is a short written description of an image, stored in the HTML alt attribute. Screen readers speak it aloud to visually impaired visitors, browsers display it when an image fails to load, and search engines read it to understand what the image shows. It is the most important element of image SEO because it is the only signal that describes the image content directly, in your own words.
A strong description is specific, natural and honest. Describe what is actually in the picture in one clear sentence, and include a keyword only when it genuinely belongs there. For a plumbing client, alt="plumber" wastes the opportunity; alt="Plumber replacing a hot water system in a Melbourne roof cavity" describes the scene and carries the topic. Purely decorative images, dividers and background flourishes should get an empty attribute, alt="", so screen readers skip past them instead of reading out clutter.
The one-line test: write alt text for the person who cannot see the image. If your description helps them picture it, it helps Google too. Keyword-stuffed descriptions read badly to both, and Google treats them as spam.
File names, formats and image optimisation
File names are the signal everyone forgets. IMG_4021.jpg tells Google nothing; colorbond-roof-restoration-geelong.jpg describes the content before the page even renders. Rename images before you upload them, using lowercase words separated by hyphens. It takes seconds per image, and across hundreds of pages it compounds into a meaningful signal.
Format and compression are where the speed lives. Modern formats such as WebP and AVIF typically produce far smaller files than JPEG or PNG at the same visual quality, and most CMS platforms and CDNs can convert them automatically. Photos belong in JPEG or WebP, logos and sharp-edged graphics in PNG or SVG. Then compress everything: image optimisation is mostly the unglamorous work of squeezing file sizes down before upload, and free tools like Squoosh or TinyPNG handle it in bulk. A hero image that arrives at 300 KB instead of 4 MB changes how the whole page feels.
Image SEO and Core Web Vitals
Images are the heaviest thing on most pages, which makes image SEO inseparable from performance. Three habits do most of the work. First, always set width and height attributes so the browser reserves space and the layout does not jump around while images load. Second, lazy-load images below the fold with loading="lazy", but never the hero image, because delaying the largest visible element hurts your loading score rather than helping it. Third, serve responsive sizes with srcset so a phone is not forced to download a desktop-sized file. Our technical SEO checklist covers these checks alongside the rest of the site health items.
Google Images, sitemaps and structured data
If images matter to your business, help Google find them. An image sitemap, or image entries inside your existing sitemap, tells crawlers exactly which files belong to which pages. Structured data goes further: product schema with an image property is what puts your photos into rich results, which is why image SEO carries extra weight in product page SEO and across eCommerce SEO generally, where the photo often is the click. Captions and nearby text matter too, because Google reads the context around an image to confirm what it shows.
The quick-win image SEO checklist
Work through this list on your most important pages first, then sweep the rest of the site:
- Every meaningful image has a descriptive alt attribute; decorative images have an empty one.
- File names describe the subject in lowercase hyphenated words, set before upload.
- Photos are served as WebP or compressed JPEG; logos and icons as SVG or PNG.
- Every image is compressed, with the largest files tackled first.
- Width and height attributes are set on every image to prevent layout shift.
- Below-the-fold images lazy-load; the hero image does not.
- Responsive srcset sizes are in place for large images.
- Product and key content images appear in the sitemap and in structured data.
None of this is difficult, which is exactly why it works: image SEO rewards the site that simply does the housekeeping. An afternoon on the checklist above will put you ahead of most competitors, because most of them have never opened their media library with SEO in mind.
Want the full picture? Images are one part of the audit. Run our free SEO audit to see every quick win on your site, or talk to us and we'll prioritise the fixes for you.
