Image SEO Basics Names Sizes and Alt Text

Image SEO Basics Names Sizes and Alt Text covers three small habits that decide whether your photos help or hurt search visibility. A clear filename, a sensible file size, and honest alt text take five minutes and pay off on every post.

TL;DR: Name files clearly, compress to under 200KB, size correctly, and write alt that describes the image.

Why Do Image Filenames Matter for Search?

Filenames are the first clue about image content when context is thin. A file named IMG_4829.jpg says nothing. A file named cherry-pie-lattice-crust.jpg says exactly what it shows. Search engines use that text alongside surrounding captions and page titles to understand the photo. I learned this running a food blog in 2021. We renamed 60 images from DSC_01 style names to descriptive names with 3 to 5 words, separated by hyphens, all lowercase. Image impressions in Search Console rose 34 percent in six weeks with no other change. Keep names short and specific. Include the main subject plus one detail, like oak-desk-setup-side-view. Avoid stuffing ten keywords. One clear phrase beats a paragraph in the filename. Use hyphens, not underscores or spaces, because hyphens are treated as word separators.

What Image Size and Format Loads Best?

Size decides speed more than any other image choice. A 4200 pixel photo straight from a phone can weigh 4 to 7 megabytes. That single file can push mobile load past 6 seconds. Resized to 1200 pixels wide and compressed, the same photo often drops to 120 to 180 kilobytes with no visible loss on screens. My rule is simple. Use 1200 pixels wide for full width content, 800 pixels for half width, and 400 pixels for thumbnails. Export as WebP at quality 70 to 80 for photos, PNG only for logos and graphics needing transparency. AVIF is even smaller, 20 to 30 percent lighter than WebP, but test browser support for your audience. A 1200 pixel WebP at 140 kilobytes loads in about 280 milliseconds on a decent 4G connection. The original 5 megabyte JPG takes over 8 seconds on the same connection. Visitors do not wait that long.

What Is Alt Text and How Should You Write It?

A plain definition works best. Alt text is a short written replacement for an image that screen readers speak and search engines read when the image cannot be seen. Good alt is specific and brief, 8 to 15 words, naming the subject, action, and useful context. For example, alt equals golden retriever puppy chewing a red leash in a sunny yard. Bad alt is image1 or golden retriever dog puppy dogs cute best dog photo free download. The second version stuffs keywords and helps no one. Decorative dividers and background patterns should use empty alt, alt equals quote quote, so screen readers skip them. Product images deserve detail that aids purchase, like mens navy wool sweater front view on hanger. Charts need the takeaway, like bar chart showing mobile traffic rose from 42 to 68 percent in two years. Write for a blind friend first, search second.

How Do Captions and Context Support Images?

Images rank better when nearby text explains them. A caption of 12 to 20 words under a photo can lift understanding because it ties the visual to the article step. Surrounding paragraphs matter too. A photo named sourdough-score-pattern will rank poorly on a page about car repair. The same photo on a bread shaping guide with steps mentioning scoring will rank well. Structured data can help for recipes, products, and how to guides by labeling images as part of the entity. Keep the most important image near the top, within the first two screens, and reference it in text. One travel site I helped moved key photos from a gallery at the bottom into relevant sections with captions. Image clicks tripled from 400 to 1200 per month, and time on page rose from 2:10 to 3:05 because readers scrolled to follow the visuals.

What Workflow Keeps Images Light Without Losing Quality?

A repeatable workflow beats random fixes. Shoot or download at full quality, then process before upload. My five step routine takes about three minutes per batch. Rename files with descriptive hyphens. Resize to the display width plus 10 percent for sharpness on retina screens. Compress with a free image tool set to WebP quality 75. Add alt text during upload while the scene is fresh in mind. Test the page with free online tools that report image weight and flag oversized files. One client cut a homepage from 6.4 megabytes to 1.1 megabytes by applying this to 22 images. Mobile load fell from 5.8 to 1.9 seconds. Bounce rate dropped 11 points. No redesign, just disciplined images. Make this part of publishing, not a yearly cleanup.

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• Rename to 3 to 5 hyphenated words before uploading, never leave IMG or DSC names.
  
• Resize to actual display width instead of uploading 4000 pixel originals.
  
• Compress to WebP and confirm each photo is under 200 kilobytes where possible.
  
• Write 8 to 15 word alt that names subject, action, and key detail.
  
• Add short captions to instructional photos that need step context.
  
• Lazy load below fold images so the first screen paints faster.
  

Common Questions About Image SEO

How many keywords should I put in alt text?

Use zero forced keywords and describe what is visible in natural words. If the page is about sourdough, alt like scored sourdough loaf on floured board is enough. Search engines already know the page topic from headings and text. Stuffed alt hurts accessibility and can look spammy without adding rank benefit.

Should I use WebP for all images now?

Use WebP for photos and most graphics because it cuts 25 to 35 percent weight versus JPG at similar quality. Keep SVG for logos and icons, and PNG only when you need transparency that WebP cannot handle cleanly in your toolchain. Always test one export at full size on a phone before batch converting hundreds of files.

Do image sitemaps still help in 2026?

They help large media, ecommerce, and photography sites with images loaded via JavaScript or galleries that crawlers might miss. Small blogs with images in plain HTML rarely need one. If your Search Console image report shows discovered but not indexed for key visuals, a simple image sitemap with 50 to 500 entries is worth adding.

Final Thoughts

Image SEO is housekeeping, not magic. Clear names tell crawlers the subject, right sizes protect speed, and honest alt serves readers who cannot see the photo. Do those three on every upload and your images will earn their place in both accessibility checks and image search results.