Image SEO — The Complete Technical Checklist

Images affect SEO in two ways: they can rank independently in Google Image Search (driving traffic directly), and they impact page speed (which affects Core Web Vitals and overall ranking). Getting both right requires a specific checklist — this is it.

1. File Names — More Important Than Most People Think

Google reads file names. IMG_3847.jpg tells Google nothing. red-leather-office-chair.jpg tells Google exactly what the image shows.

Rules for image file names:

• Use lowercase letters and hyphens only (no underscores, no spaces)
• Include your primary keyword naturally: how-to-compress-jpg-online.png
• Be descriptive but not stuffed: 3-5 words is ideal
• Match the file name to the image content — don't keyword-stuff irrelevant images

2. Alt Text — The Single Most Important Image SEO Element

Alt text serves two purposes: accessibility (screen readers) and SEO (telling search engines what the image depicts). Both matter. Write alt text that describes the image accurately, includes relevant keywords naturally, and reads like a sentence — not a keyword list.

For decorative images (spacers, dividers, purely aesthetic elements), use empty alt text: alt="". This tells screen readers to skip it without creating noise.

3. Image File Size — The Speed-Ranking Connection

Large images slow down pages. Slow pages hurt rankings. Google's Core Web Vitals (especially LCP — Largest Contentful Paint) are directly affected by how fast your largest above-the-fold image loads.

Target file sizes by context:

4. Image Dimensions — Serve the Right Size

Never serve a 4000×3000px image in a 400×300px container. The browser has to download all those extra pixels just to throw them away. Use responsive images with the srcset attribute, or ensure you resize images before uploading.

Practical approach: resize your images to the maximum display dimensions on your site before uploading. A blog post content area that's 800px wide never needs an image wider than 1600px (for 2× retina displays).

5. Structured Data for Images

For product images, recipes, articles, and other rich result types, adding structured data (Schema.org) helps Google understand and feature your images in enhanced search results. Recipe images appear in recipe carousels. Product images appear in shopping results. The investment is worth it.

6. Image Sitemaps

Include image information in your XML sitemap using the image sitemap extension. This helps Google discover and index your images faster, especially for pages with many images or images loaded via JavaScript.

7. Lazy Loading

The loading="lazy" attribute tells browsers to defer loading off-screen images until the user scrolls toward them. This dramatically improves initial page load time. Add it to every image that isn't in the initial viewport: <img src="..." alt="..." loading="lazy">.

8. WebP and AVIF Adoption

Serving modern formats (WebP, AVIF) reduces file sizes by 25-50% vs JPEG/PNG. Smaller images = faster loading = better Core Web Vitals = better rankings. The performance benefit is now a direct ranking factor via the Core Web Vitals assessment.