Image SEO for catalogs
Alt text, file names, formats, compression and dimensions decide whether product photos win traffic from Google Images or quietly drag your store down. Here is how we handle them.
On an online store, product photography is the content. A catalog can carry thousands of images, and each one is both a ranking signal and a weight on the page. Handled well, images earn traffic through Google Images, reinforce the relevance of a product page and keep it fast. Handled carelessly, they become the single biggest reason a page loads slowly and slips in the rankings. Image SEO is not an afterthought bolted onto a store; it is a small optimization problem you solve the same way on every SKU.
Alt text that describes, not stuffs
The alt attribute exists first for accessibility: it is what a screen reader announces and what shows when an image fails to load. Google reads it as one of the main clues to what an image depicts, which is why it matters for ranking in Google Images. Write it the way you would describe the photo to someone who cannot see it, in plain language, including the attributes a shopper would actually search for.
- Describe the product concretely: navy leather Chelsea boot, side view beats boot or IMG_2043.
- Include natural attributes like color, material and model without repeating the keyword five times.
- Leave alt empty (alt="") on purely decorative images so assistive tech skips them.
- Do not open every alt with "photo of" or "image of" — it adds nothing.
File names carry meaning too
Search engines read the file name before they ever see the pixels. chelsea-boot-navy-leather.webp tells Google something; DSC_0098.jpg tells it nothing. Rename files at export, separate words with hyphens, keep them lowercase, and avoid spaces or accented characters that get percent-encoded in the URL.
Formats and compression: WebP and AVIF
Most catalogs still ship oversized JPEG and PNG files. Modern formats do the same job at a fraction of the weight. WebP is supported in every current browser and typically cuts file size by a quarter to a third versus a comparable JPEG; AVIF compresses even harder, though it encodes more slowly and older devices may need a fallback. The practical rule: serve AVIF or WebP with a JPEG fallback, and never ship a PNG for a photograph — reserve PNG for logos and flat graphics with transparency.
- Compress to a visually lossless target (around quality 75–85) instead of maximum quality.
- Export at the real display size — a 3000px master feeding a 600px slot is wasted bandwidth.
- Use the <picture> element or your platform's image API to negotiate the best format per browser.
Dimensions, srcset and layout shift
Always set explicit width and height attributes (or a CSS aspect-ratio) on every image. Without them the browser cannot reserve space, content jumps as images arrive, and you fail Cumulative Layout Shift — one of the Core Web Vitals Google measures. Then use srcset and sizes to hand each device an appropriately sized file: a phone should never download the desktop hero. This is the highest-leverage image work you can do for page speed.
Lazy-loading, without breaking the fold
Add loading="lazy" to below-the-fold images so the browser defers them until the shopper scrolls near. Do the opposite for the one image that matters most on load — the main product shot or hero. Mark it fetchpriority="high" and never lazy-load it, or you will slow your Largest Contentful Paint. On a product page that means the primary image loads eagerly while gallery thumbnails and related-product tiles load lazily.
A repeatable catalog checklist
- Descriptive, unique alt text on every meaningful image; empty alt on decorative ones.
- Readable, hyphenated, lowercase file names set at export.
- AVIF or WebP with fallback; no PNG photographs; quality tuned, not maxed.
- Explicit width and height on every image; responsive srcset and sizes.
- Eager-load the LCP image; lazy-load everything below the fold.
- List product images in an image sitemap so Google can discover them.
None of this is exotic — it is discipline applied across every SKU. When we audit product pages for a Florida store, images are usually where the fastest wins hide: lighter pages, better Core Web Vitals and a second stream of visitors arriving straight from Google Images.
Image SEO, quick answers
Does alt text really affect rankings?
Indirectly for web results and directly for Google Images. Alt text tells Google what the picture shows, so accurate, descriptive alt helps images surface in image search and adds context to the page. It is not a place to stuff keywords — write it for a person who cannot see the photo.
Should I use WebP or AVIF?
Both beat JPEG and PNG on weight. WebP is the safe default: universally supported and much lighter. AVIF compresses even more but encodes slower and needs a fallback for a few older clients. Serving AVIF or WebP with a JPEG fallback via the picture element gives you the best of both.
Why do my images cause layout shift?
Because the browser does not know how tall an image will be until it downloads. Set explicit width and height attributes, or a CSS aspect-ratio, on every image so the space is reserved up front. That single fix usually clears most Cumulative Layout Shift problems on a catalog.
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MKS US Consulting is a Miami-based SEO agency, deliberately kept at a human scale. From our studio on Brickell Avenue we partner with e-commerce brands across Florida, from Miami and Miami Beach to Fort Lauderdale, Boca Raton, Orlando and Tampa, to grow the organic visibility that brings qualified, ready-to-buy traffic. Small enough to know every page of your catalog, senior enough to move the rankings that decide a quarter.
Search is our craft, and our own calling card: the way our clients find us on Google is exactly how we make their stores found by their customers. No rented audiences, no paid dependency, just organic traffic that compounds. If you sell online in Florida and want a partner who treats your visibility like an asset, let's talk.