Image SEO: Alt Text, File Names, and Compression Explained

If you run a small business website in Melbourne, there is a good chance every photo and logo on your site is quietly working against you. Unoptimised images are one of the most common technical SEO problems we see during audits — oversized files slow pages down, meaningless file names tell Google nothing, and missing alt text hands away free traffic from Google Images. The good news is that image SEO is one of the easier technical fixes once you understand the basics. This guide covers file names, alt text, compression and format choice, plus responsive images and lazy loading, in plain English with real 2026 data. If you’d rather have a specialist look at your whole site first, claim your free SEO audit and get a prioritised list of fixes.

Why Image SEO Actually Matters

Image SEO covers everything that helps search engines understand, index and rank the images on your website, plus everything that helps those images load fast for real visitors. It sits alongside foundations like clean header tags, internal linking and HTTPS, but gets skipped more often because images feel like a design job rather than an SEO job.

The opportunity is bigger than most Melbourne owners realise. Image-based queries make up around 22% of all Google searches, and Google Lens (Google’s visual search tool, letting people search using a photo instead of typed words) handled more than 20 billion monthly visual searches in 2025–2026, up from around 3 billion in 2021 (Source: Backlinko, 2026). If your tradie, retail or hospitality site has no image strategy, you are invisible in that channel entirely.

Images are also the biggest contributor to page weight (the total size of everything a browser downloads to show your page). On a typical mobile homepage, images alone account for roughly 911 KB of data, more than any other resource type (Source: HTTP Archive Web Almanac, 2025). Every kilobyte you shave off is a kilobyte visitors do not wait for, and speed is a confirmed Google ranking signal.

Start With Descriptive File Names

Before you touch alt text, look at the file name of the image you are about to upload. A photo straight off your phone will usually be called something like IMG_4021.jpg or DSC00456.png, which tells Google, and anyone browsing your image URL, precisely nothing about what is in the picture.

Rename every image before uploading, using lowercase words separated by hyphens that describe what it shows. Google’s own documentation confirms file names are a genuine signal it uses to understand an image (Source: Google Search Central, 2026):

• Bad: IMG_20260115_093211.jpg — Good: melbourne-cafe-fitout-before-after.jpg
• Bad: photo1.png — Good: plumber-hot-water-system-installation-melbourne.png
• Bad: image-final2.jpg — Good: custom-timber-kitchen-splashback-richmond.jpg

Keep names concise, four to seven words is usually enough, and avoid stuffing every keyword you can think of into one file name. One or two natural, relevant terms plus a locality where appropriate beats a wall of hyphenated keywords.

Alt Text: Where Accessibility and SEO Meet

Alt text (short for “alternative text”) is a short description added to an image’s HTML code, read aloud by screen readers for vision-impaired visitors and shown if the image fails to load. It is also one of the clearest signals search engines use to understand what an image depicts, since they cannot “see” a photo the way a person can.

Good alt text describes the image in context, what it shows and why it is on that page, rather than repeating a keyword. Aim for roughly 80 to 125 characters: enough detail to be useful, short enough that a screen reader user is not stuck listening to a paragraph. Write unique alt text for every image; copying the same description across a gallery defeats the purpose for both accessibility and search engines.

• Poor: plumber Melbourne plumber Melbourne cheap plumber
• Better: Licensed plumber installing a hot water system in a Melbourne home

Purely decorative images, background textures, dividers, spacer graphics, should generally use an empty alt attribute (alt="") so screen readers skip them, rather than a forced, meaningless description. Reserve descriptive alt text for images that carry real information: products, team photos, completed jobs, diagrams and infographics.

Choosing the Right Image Format and Compression

Once file names and alt text are sorted, the next lever is compression: reducing an image’s file size either by removing invisible data (lossless) or slightly reducing quality in ways the eye barely notices (lossy). The format you save in has a huge effect on how small a file can get without looking worse.

Two newer formats, WebP and AVIF, generally produce smaller files than older JPEG and PNG formats at equivalent visual quality. WebP already accounts for a meaningful share of image bytes served across the web, and AVIF is growing the fastest of any image format (Source: HTTP Archive Web Almanac, 2025). Despite that, JPEG remains the format used on more than half of desktop pages, largely out of habit.

Format	Typical File Size	Best Use Case	Browser Support
JPEG	Medium (baseline)	Photos with lots of colour and detail, e.g. team or product photography	Universal — every browser and device
PNG	Large	Logos, icons and graphics that need a transparent background or sharp edges	Universal — every browser and device
WebP	25–35% smaller than JPEG at similar quality	General-purpose replacement for most JPEGs and PNGs on the web	All modern browsers (Chrome, Edge, Firefox, Safari 14+)
AVIF	Often 30–50% smaller than WebP at similar quality	Hero images and other large, high-impact photos where every kilobyte counts	Most modern browsers; slightly less consistent than WebP on older devices

In practice, export new images as WebP by default, reserve AVIF for performance-critical hero banners, and keep PNG only for logos needing transparency. Whatever format you choose, resize the image to the dimensions it will actually display at — a 4000-pixel-wide photo squeezed into a 400-pixel box is wasted data every load. Unsure how your site stacks up? Run a basic technical SEO audit yourself, or simply get a free SEO audit from our team.

Responsive Images and Lazy Loading, Explained Simply

Two more concepts matter once formats and compression are sorted. Responsive images means serving different sized versions of the same photo depending on the visitor’s device, a phone gets a smaller file than a widescreen monitor, since it does not need the extra detail. This is usually handled through the HTML srcset attribute, which most modern content management systems, including WordPress, generate automatically once images are uploaded at a sensible size.

Lazy loading means telling the browser to delay loading images further down the page until the visitor scrolls near them, rather than loading everything the instant the page opens, cutting the data a visitor downloads on their first visit. Most browsers support this natively with a loading="lazy" attribute, no plugin required. The exception is your hero image, the main one visible without scrolling; it should load immediately, since it is often the element that determines your Largest Contentful Paint score, discussed below.

How Image SEO Affects Google Images Traffic and Core Web Vitals

Core Web Vitals are three metrics Google uses to judge how a page feels to use: loading speed, visual stability and responsiveness to taps. The loading speed metric, Largest Contentful Paint (LCP), measures how long the biggest visible element, often a hero image, takes to fully render. Slow, unoptimised images are one of the most common causes of a poor LCP score, and Google has confirmed page experience factors into ranking.

The commercial impact is not theoretical. In an official case study, Vodafone Italy A/B tested two otherwise identical landing pages and found a 31% improvement in LCP, achieved partly by resizing the hero image, led to an 8% increase in sales, plus double-digit gains in cart and lead conversion (Source: web.dev, 2026).

Beyond speed, well-optimised images with genuine alt text and file names are also what let you rank in Google Images and visual search at all. With Google Lens now handling more than 20 billion visual searches a month, treating image optimisation as “nice to have” rather than core SEO work leaves an entire, fast-growing channel untapped (Source: Backlinko, 2026).

A Simple Starting Checklist

If your image library has been neglected for a while, do not try to fix everything at once. Start with the pages that matter most commercially — your homepage, key service pages and top product pages — and work through this order:

1. Rename any obviously meaningless file names (IMG_1234.jpg style) on your most important pages first.
2. Add or rewrite alt text for every meaningful image, keeping descriptions under about 125 characters.
3. Re-export oversized images as WebP (or AVIF for hero banners), resized to their actual display dimensions.
4. Confirm lazy loading is switched on for below-the-fold images, and switched off for your hero image.
5. Check your Core Web Vitals scores in Google Search Console or PageSpeed Insights, and re-test after each batch of changes.

Image SEO is easy to put off because it feels tedious rather than difficult, but for a Melbourne small business competing for local search visibility, it is genuinely low-hanging fruit. Descriptive file names and alt text cost nothing but a few minutes of attention, and the payoff shows up in both Google Images traffic and Core Web Vitals scores. This is exactly the kind of technical work our team folds into every engagement, alongside the broader foundations covered in our SEO services. If you would like an expert to review exactly which images are costing you rankings and speed, learn more about our Melbourne-based team or claim your free SEO audit today.