What image SEO actually is
Image SEO is the set of practices that help your images get found by Google Image Search, render fast for users, and contribute to the ranking of the page they sit on. Six elements do almost all the work:
- The filename of the image file itself.
- The alt text stored in the
altattribute. - The image format (WebP, JPEG, PNG, SVG, AVIF).
- The file size, controlled by compression.
- The dimensions, set explicitly in HTML or CSS.
- Whether the image lazy-loads when below the fold.
None of these are advanced. All of them are ignored on most Perth small-business sites we audit. A typical site has 60 to 300 images uploaded directly from a phone, named IMG_2384.jpg, weighing 4MB each, with no alt text. Every one of those images is a small SEO debt the site is paying every time Google crawls it.
Why it matters in 2026
Three reasons image SEO has become more important, not less, over the last two years.
Image Search is a real traffic source on visual industries. If you sell anything where customers want to see it (homewares, fashion, food, real estate, interiors, fitness, automotive), Google Images sends meaningful traffic. We have one Perth client whose Google Images traffic is 22 percent of total organic. Two of their competitors get effectively zero from Images because their alt text is empty. Same products, same market, very different exposure.
Core Web Vitals reward image discipline. The Largest Contentful Paint (LCP) metric is almost always the hero image on a page. A 3MB hero takes too long to render, LCP times out, your Core Web Vitals drop, and Google uses CWV as a tiebreaker on close ranking decisions. The Core Web Vitals pillar covers this in detail. Image compression is the first lever to pull.
AI Overviews and image-aware AI engines pull from your images. Google's AI Overviews, Perplexity and ChatGPT Search increasingly cite images alongside text. Pages with well-described, structured images get cited more often. Image SEO is becoming entity SEO for the visual layer. See entity SEO for the AI era for the related text-side practice.
The six rules of image SEO
Rule 1: Use descriptive filenames
Rename images before uploading. IMG_2384.jpg tells Google nothing. emergency-electrician-van-perth.jpg tells Google what is in the image and gives the file a keyword. Use lowercase, hyphens between words, no spaces, no underscores. Keep filenames short (5 to 8 words max) and descriptive.
Rule 2: Write real alt text
Every meaningful image needs an alt attribute describing what it shows. Decorative images (background patterns, decorative borders) should have alt="" (empty, explicitly set) so screen readers skip them. Writing alt text properly is the section below.
Rule 3: Use modern formats
WebP is the default for almost everything. JPEG is fine for photos if WebP is genuinely not available. PNG only when you need transparency or text crispness (logos, screenshots with fine text). SVG for icons and logos. AVIF if you want to push the compression further and your CMS supports it. The format choice affects file size more than any other single setting.
Rule 4: Compress to under 200KB
Target file sizes:
- Hero images: under 200KB. Ideally 100 to 150KB.
- Inline content images: under 100KB.
- Thumbnails: under 30KB.
- Icons (SVG): under 5KB.
Anything over 500KB is hurting your page speed. Run every image through Squoosh, TinyPNG or your CMS's compression plugin before publishing.
Rule 5: Set explicit width and height
Add width and height attributes to every img tag, even when the image is responsive:
<img src="van.webp" width="1200" height="800" alt="Brand emergency electrician van Perth">This lets the browser reserve the right amount of space before the image loads. Without dimensions the layout shifts when images arrive, which destroys your Cumulative Layout Shift (CLS) score. Even one bad image can drop CLS into the red.
Rule 6: Lazy-load below-the-fold images
Add loading="lazy" to every image that is not visible on initial page load. Native lazy loading is supported by every modern browser:
<img src="testimonial.webp" alt="..." loading="lazy" width="600" height="400">Do not lazy-load the hero image. The hero is usually the LCP candidate, and lazy-loading it adds a delay that hurts the metric.
Writing alt text that works for SEO and screen readers
Alt text serves two audiences. The blind user listening to a screen reader. And Google's image indexer. Both want roughly the same thing: a clear, concise description of what is in the image and why it matters in context.
The structure
Five-word to fifteen-word description, written as a complete idea, that names the subject and its relevant context. Skip "image of" or "picture of" because the screen reader already announces "image" before reading the alt.
Examples:
- Bad:
alt="IMG_4271". Completely empty signal. - Bad:
alt="van". Too vague. - Bad:
alt="Best emergency electrician Perth WA cheap fast service 24/7 plumbing electrical". Keyword stuffing, painful for screen reader users. - Good:
alt="Brand emergency electrician van parked in front of a Perth residential property". Descriptive, includes natural keywords, reads like a sentence.
When to use empty alt
Decorative images (background patterns, divider lines, purely aesthetic photos that add no content) should have alt="". The empty alt tells screen readers to skip the image entirely. Omitting the alt attribute is different from setting it empty; omitting it makes screen readers read out the filename, which is worse than skipping.
Alt text vs caption
The alt attribute and the visible caption (<figcaption>) are different. Alt text describes the image for users who cannot see it. The caption adds context everyone can read. Often the alt text mirrors the caption but does not have to. Use both where the image is content (a chart, a product photo, a key example) and the caption adds explanation.
Common mistakes
- Rename every image before uploading, even if the CMS does it for you.
- Write the alt text in the same upload step. Never plan to "go back and add alt".
- Pick WebP as the default export from Photoshop, Figma or Canva.
- Use Squoosh or TinyPNG for one-off compression. Use a plugin for bulk.
- Set width and height on every img tag without exception.
- Add lazy loading to every below-fold image.
- Uploading 4MB hero images straight from the camera roll.
- Filenames like
Screen Shot 2025-08-12 at 11.42.05 am.png. - Empty alt attributes on content-bearing images (silent for screen readers, no SEO signal).
- Stuffing alt text with every keyword you wish you ranked for.
- Using PNG for photos (twice the file size of JPEG for no visual benefit).
- Hot-linking to images on other sites instead of hosting your own.
- Forgetting the alt on the hero image, where it would carry the most weight.
Tools and checklists
- Squoosh. Free, browser-based. Drag in a JPEG, pick WebP, slide compression to taste, download. Great for one-offs and learning the trade-offs.
- TinyPNG. Free up to 20 images per batch, paid for bulk. The default for most teams. Handles JPEG, PNG and WebP.
- ShortPixel or Imagify. WordPress plugins. Compress every image on upload automatically and convert existing media library entries to WebP. Set and forget.
- Screaming Frog. Crawl your site, sort by missing alt text. Catches every untagged image in one report.
- Lighthouse. The Chrome DevTools audit flags oversized images, missing alt, missing dimensions and missing lazy loading. Run it on every new page.
- Our free SEO audit tool. Flags image SEO failures alongside everything else in a one-click report.
Pre-upload checklist (60 seconds per image)
- Filename is descriptive, lowercase, hyphenated, under 8 words?
- Format is WebP (or SVG for icons, JPEG as fallback)?
- File size under target (200KB hero, 100KB inline)?
- Dimensions correct for the layout, not 2x or 3x oversized?
- Alt text written: 5 to 15 words, descriptive, no keyword stuffing?
- Width and height attributes added to the img tag?
- loading="lazy" added if below the fold?
Perth and WA context
Real estate. Real estate sites live on images. A Perth agency site we audited had 4,200 listing photos averaging 2.8MB each, all named property-photo-XXXX.jpg, all with empty alt. We migrated them to WebP at an average 280KB and rewrote alt text to follow the pattern "[bedrooms]bed [type] in [suburb], [feature]". Image Search traffic to listings rose by about 180 percent over four months. The fix was bulk-scripted in an afternoon. For broader real-estate context see real estate SEO.
Trades. Perth electricians, plumbers and builders often have project photo galleries that are pure dead weight in terms of SEO. We rename them to before-after-kitchen-rewire-fremantle.webp with alt text like "Kitchen powerpoint upgrade Fremantle, completed by Brand in 2025". Google starts surfacing them in Image Search for both the trade query and the location query. See trades SEO and SEO Fremantle for the local examples.
Mining services. Industrial sites typically have equipment photos that are completely uncategorised. We add alt text naming the specific equipment ("Caterpillar 793F haul truck on Pilbara iron ore site") and Image Search starts driving B2B research traffic. The mining SEO guide and the Karratha SEO page cover the regional patterns.
Hospitality. A Fremantle cafe we worked with had Instagram-quality food photos buried in their site with no alt text. Adding food-name alt text ("Pulled pork brioche burger with kimchi and fries, served at Brand Cafe Fremantle") brought meaningful Google Images traffic for menu-item searches. Three hours of alt-text writing produced sustained traffic for over a year.
For the broader page-speed picture that image work feeds into, see the Core Web Vitals pillar. For the parent on-page playbook that image SEO sits inside, return to On-Page SEO.