Image SEO Best Practices: Optimizing Alt Text, Formats, and Load Speed

Write alt text for a person, not a crawler

Alt text is an accessibility attribute that search engines happen to read. Someone using a screen reader hears it in place of the picture, so the test is simple: does this sentence tell them what they are missing? "Tan leather Chelsea boot, side view, showing the elastic panel" passes. "boots leather boots buy boots online womens boots" fails, and reads as spam to both audiences.

Keep it to a normal sentence. Say what is in the image and why it is on this page. If the image is purely decorative, a background texture or a divider, give it an empty alt attribute rather than a description. An empty alt is a real instruction that tells a screen reader to skip it. Leaving the attribute off entirely is different and worse, because some readers then announce the filename instead.

Filenames and the words around the image

A filename is a weak signal but it costs nothing to get right. Rename IMG_4471.jpg to chelsea-boot-tan-side.jpg before you upload and you have spent four seconds. Do not stuff it. A filename with nine hyphenated keywords in it looks exactly like what it is.

The text immediately around the image does more work than the filename does. A caption, the paragraph the image sits next to, the nearest heading: these are what an index uses to work out what the picture is of and whether the page is a reasonable answer to a query. An image dropped into a wall of unrelated text has very little to go on.

Product images have their own rules

For a shop, the image is often the thing that decides the sale, and the same choices that help a buyer help the listing. Give every variant its own photograph rather than recolouring a description; a shopper who sees the wrong colour will bounce, and bounces are visible. Keep framing and background consistent across a range so a grid of results looks like a catalogue rather than a car boot sale. Include something that conveys scale for anything where size is ambiguous.

On the markup side, product structured data with an image field is what lets your photograph appear alongside the listing in richer search results. It is a prerequisite, not a guarantee, and it only helps if the image URL it points at is actually reachable by a crawler.

Make them load properly

• Put width and height attributes on every img tag. The browser then reserves the right amount of space before the file arrives, and the page stops jumping around as things load.
• Use lazy loading for images below the fold, and never on the main image at the top. Lazy loading the first thing a visitor sees delays the very element your loading score is measured against, which is a surprisingly common own goal.
• Add a srcset so a phone downloads a phone sized file. A single desktop image served to every device wastes the bandwidth of the visitors most likely to be on a slow connection.
• Resize before uploading rather than constraining with CSS. An image styled to 900 pixels wide still downloads all 4032 pixels of the original. The compression guide covers where the real savings are.

Things that quietly hold you back

Stock photography is the big one. If the same library shot appears on four hundred other sites, there is no reason for yours to be the result anyone is shown, and nothing in your alt text changes that. Your own photographs, even imperfect ones, are the only images on your site that are genuinely yours.

After that come the technical blocks. Images that only load after a click or a scroll driven script may never be seen by a crawler. An image directory disallowed in robots.txt cannot be indexed no matter how good the markup is. Images hosted on a subdomain or a CDN you have not verified can be indexed in a way that separates them from your pages. None of these are exotic, and all of them are worth checking once before you spend a month writing better alt text.

One thing to watch when you optimise

Any browser based converter, this site included, decodes your image and writes a new file from the pixels. Nothing copies the metadata across, so the output has no EXIF block: no camera data, no capture date, no GPS, and no embedded copyright or IPTC credit fields. Stripping location data before publishing is often exactly what you want. Losing your own attribution fields on a photograph you licence out is not, so process a copy and keep the original.

What to expect from all this

Getting images right makes a page faster, more accessible and more likely to be shown for the queries it already deserves. It does not make a thin page rank for a term it has no claim to, and traffic arriving from image search tends to behave differently from traffic arriving from a text result, so measure the two separately before drawing conclusions. The work is worth doing. It is just worth doing with accurate expectations.

When you are ready to act on it, the image compressor and image resizer here handle a batch in one pass, and both run entirely inside your browser, so unreleased product photography never leaves your machine on the way to being optimised.