Why Image SEO Is Often Ignored — and Why That Is a Mistake
Most SEO guides focus on keywords, backlinks and content length. Images get a passing mention at best. But unoptimized images are one of the most common reasons a page loads slowly — and page speed is a confirmed Google ranking factor. On top of that, Google Images drives significant search traffic that most site owners never capture.
Getting image SEO right takes about 10 minutes per page and can improve your Core Web Vitals score, your Google Images visibility, and your accessibility score all at once.
Step 1: Use Descriptive File Names
Before you upload an image, rename the file. Google cannot see the image itself — it reads the file name as a signal of what the image contains.
Wrong: IMG_20240312_084523.jpg
Right: keyword-density-checker-screenshot.jpg
Use lowercase letters, hyphens between words (not underscores or spaces), and include your target keyword where it makes sense. Keep it short and descriptive — 3 to 5 words is ideal.
Step 2: Write Alt Text for Every Image
Alt text (the alt attribute in your <img> tag) serves two purposes: it tells screen readers what the image shows for visually impaired users, and it tells Google what the image contains for ranking purposes.
Good alt text is:
- Descriptive and specific — describe what is actually in the image
- Under 125 characters
- Natural — do not keyword-stuff it
- Not "image of" or "photo of" — Google already knows it is an image
Wrong: alt="seo"
Right: alt="keyword density checker showing 2.3% density for target keyword"
Decorative images (icons, backgrounds, dividers) should have an empty alt attribute: alt="". This tells screen readers to skip them.
Step 3: Compress Images Before Uploading
Large image files are one of the top causes of slow page load times. A 3MB JPEG that looks identical to a 200KB compressed version will cost you rankings. Google's PageSpeed Insights flags images as one of the most impactful fixes for page speed.
Target file sizes:
- Hero images: under 200KB
- Blog images: under 100KB
- Thumbnails and icons: under 20KB
Use WebP format where possible — it is typically 25–35% smaller than JPEG at the same quality level and is supported by all modern browsers.
Step 4: Set Image Dimensions in HTML
Always specify the width and height attributes on your <img> tags. This allows the browser to reserve the correct space before the image loads, preventing Cumulative Layout Shift (CLS) — one of Google's Core Web Vitals metrics. High CLS scores hurt rankings.
<img src="keyword-tool.webp" alt="keyword density checker tool interface" width="800" height="450">Step 5: Use Lazy Loading
Add loading="lazy" to any image that appears below the fold (below what the user sees on first load). This tells the browser to only load those images when the user scrolls near them, dramatically improving initial page load time.
<img src="blog-thumbnail.webp" alt="seo guide thumbnail" width="400" height="250" loading="lazy">Do not add lazy loading to your hero or above-the-fold images — those should load immediately.
Step 6: Add Images to Your Sitemap
Google can discover images through your page content, but adding them to your XML sitemap helps ensure they get indexed faster. Most SEO plugins handle this automatically. If you are managing your sitemap manually, use the image sitemap extension to list image URLs alongside your page URLs.
How Image SEO Connects to Page Speed
Images are typically 50–80% of a page's total file size. Fixing image optimization alone can cut your page load time by 1–3 seconds on mobile — which directly improves your Core Web Vitals scores (Largest Contentful Paint in particular) and your mobile search rankings.
Use our free Readability Checker to analyse your content quality alongside your images, and our Meta Tag Generator to ensure your image-heavy pages have correctly optimized title tags and descriptions before you publish.
Quick Image SEO Checklist
- File name includes target keyword with hyphens
- Alt text is descriptive, under 125 characters, no keyword stuffing
- Image compressed to target file size (WebP preferred)
- Width and height attributes set in HTML
- Below-fold images use
loading="lazy" - Hero image loads immediately (no lazy loading)
- Images included in XML sitemap
Image SEO takes 10 minutes to get right and can deliver real ranking improvements — especially on mobile where page speed matters most.