Image SEO: Alt Text, File Names and Compression Tips

Images are the most frequently overlooked element in on-page SEO. They affect page speed (the most common cause of poor Core Web Vitals scores), they carry their own ranking signals through alt text and file names, and they appear in Google Image Search - a source of qualified organic traffic most websites ignore entirely.

Alt text: the most important image SEO element

Alt text serves two purposes: accessibility (screen readers use it to describe images) and SEO (Google uses it to understand image content). Write descriptive alt text that naturally includes the relevant keyword. Not: 'image1.jpg'. Yes: 'keyword research spreadsheet showing search volume and difficulty scores'.

File names

Rename image files before uploading. Use descriptive, hyphenated names. Not: 'IMG_4821.jpg'. Yes: 'keyword-research-spreadsheet.jpg'. Google reads file names as additional context for image content.

Image compression and format

Convert all images to WebP format - 25-35% smaller than JPEG at equivalent quality. Compress to under 150KB for most images. Use tools: ShortPixel, Imagify or Squoosh (free). Always specify width and height attributes in HTML to prevent Cumulative Layout Shift.

Lazy loading

Add loading='lazy' to all images below the fold. This defers image loading until the user scrolls near them, significantly improving initial page load time and LCP scores.

Conclusion

Image SEO is a quick win that most websites have not addressed. Convert to WebP, compress, write descriptive alt text, use descriptive file names and add lazy loading. Those five steps will improve both your rankings and your Core Web Vitals scores.