The image alt attribute is one of the few fields that both helps visually impaired users and directly feeds image search — yet most sites either write “image1” or leave it empty, throwing away a batch of long-tail traffic.
Alt should say what the image expresses
Alt’s real job is reading the image’s content aloud for people who can’t see it. A “2026 content marketing budget allocation chart” should be written as “pie chart of the 2026 content team budget split by channel,” not “chart” or “content1.” When the semantics are clear, image search and featured snippets are more likely to cite it, and it lifts the host page’s relevance — those are alt’s two most direct payoffs.
Keywords can naturally go into alt, but cramming three or four words into one image crosses the line. Google treats keyword-stuffed alt as a spam signal — you not only fail to get image traffic but may drag down the whole page’s quality score. Keeping one alt to around 10 to 16 Chinese characters is safest: it explains the image without being flagged as cheating.
Here’s a positive-negative contrast: for the same backend screenshot, a bad alt is “backend,” a good alt is “Google Search Console screenshot showing declining impressions curve.” The latter states the key information in the image, and both screen-reader users and image search hit it accurately. When writing alt, pretend you’re describing the image to a colleague on the phone — write however you’d describe it. That’s the most practical mindset.
Separate decorative images from functional ones
Not every image deserves an alt. Purely decorative dividers, background textures, and layout-only icons should be written as alt=”” so screen readers skip them directly — neither wasting visually impaired users’ time nor creating noise. The judgment standard is simple: if this image were removed, would understanding suffer? If not, leave it empty. Many sites lose quality points because they’re full of useless alts like “picture.”
- Pure decoration (dividers, background textures): alt=”” lets screen readers skip, creating no noise.
- Images inside links: alt states the link destination, e.g., “view the content marketing playbook” rather than “arrow.”
- Infographics: alt states the core conclusion; details go into the body or long description.
- Product images: alt states product name plus key specs for precise image-search matching.
The image SEO puzzle beyond alt
Alt isn’t all of image SEO — it’s just one of four puzzle pieces. A filename like “content-distribution-funnel.png” carries one more layer of semantic signal than “img_0392.jpg”; the headings and paragraph text before and after the image help the search engine understand context; lazy loading and compression ensure loading speed, and speed itself is a ranking factor — a slow image drags down the whole page.
One often-overlooked point: when an image sits in a gallery or carousel, search engines may not reliably crawl its alt, so surrounding text and structured data matter more. All four signals should be done together rather than fixating on alt alone — single-point optimization has a low ceiling. Here are the four signals’ respective roles and practices:
Figure: Image SEO Standards: Filename, Alt, Compression, and Surrounding Text — Not One Can Be Missed — Core Points (compiled by YunyingGO)
| Signal | Purpose | Practice |
|---|---|---|
| Alt text | Describe content, feed screen readers and image search | Write what the image expresses |
| Filename | Give extra semantic signal | Hyphenated keyword naming |
| Surrounding text | Provide context | Add an explanation paragraph before the image |
| Image sitemap | Raise discoverability | Submit a dedicated sitemap |
Common alt mistake checklist
When auditing sites, the most common alt problems are just a few types; going through them once resolves most. Put these into the pre-publish checklist so new images stop falling in the traps, and fix old images in batches.
- Empty but not decorative: an infographic with no alt is unreadable by both screen readers and image search — the most typical and most wasteful.
- Writing useless words like “image” or “photo”: zero information; better to leave it empty.
- Keyword stuffing: five words crammed into one banner, judged as spam and hurting the whole page.
- Mixed-language text with no spaces: screen readers stumble over the phrasing, bad experience.
- All images sharing the same alt: shows you didn’t seriously write them, and search engines can tell the sloppiness.
How to engineer alt into the workflow
Relying on people to remember writing alt doesn’t last; it has to go into the process. Make alt required in the CMS upload component — block publishing if empty; give decorative images a separate “decorative” switch that auto-outputs alt=””. Add another rule: warn before publishing if an alt is under four characters or contains words like “image” or “photo.”
Scan existing images with a script in batches, manually supplementing news images and charts first and batch-emptying decorative ones. On a site of a few hundred pages, focusing on the article images in the traffic top 50 gives the highest marginal return — no need to clean everything at once.
Extra notes for mobile images
Above-the-fold image size on mobile directly determines LCP — no matter how good the alt, an image that takes three seconds to load is wasted. The practice is responsive sizing plus AVIF/WebP compression for above-the-fold images, and lazy loading for the rest. Image SEO and speed SEO are two sides of one thing; optimizing them separately drags each other down.
One more detail: on mobile, many images are cropped for display by CSS, but search engines may still crawl the original image’s alt. Keep the original and the displayed image semantically consistent — don’t show a product while the original is an unrelated stock image. Such inconsistency gets judged low quality and drags down the whole page score.
Alt and ecommerce product images
Ecommerce sites have huge image volumes, where alt’s marginal return is highest. Product-image alt should be “brand plus model plus key attribute” — for example, “Xiaomi air fryer 5L with viewing window” — catching both product searches and long-tails. When generating in batches, use templates filling in attribute fields rather than hand-writing each one.
Product images should also get structured data (Product type), feeding price, stock, and ratings to search engines for rich results. Alt solves readability; structured data solves displayability. With both stacked, a product page’s click-through rate visibly rises, especially in home and electronics categories.
