How does an SEO company optimize images?
It works on two fronts at once. One is weight: making image files smaller and sized to how they are displayed, so pages load faster. The other is meaning: making sure Google can find each image and understand what it shows, so the image helps the page and can appear in image search. Google’s image SEO best practices set out the rules for the second front, and a few of them are easy to miss.
Making Google able to find the image
Google finds images in standard HTML image elements. Its guidance is direct: “Google can find images in src attribute of element (even when it’s a child of other elements, such as the element). Google doesn’t index CSS images.” An image set as a background through CSS can look identical to a visitor and still be invisible to image search. An SEO company should check which important images on your site are loaded this way.
Format matters for the same reason. Google lists the formats it supports in the src attribute: “BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF.”
An image sitemap helps Google discover images it might otherwise miss, and Google notes that, unlike regular sitemaps, image sitemaps can include image URLs from other domains, which suits sites that serve images from a content delivery network.
Telling Google what the image shows
Alt text carries the most weight. Google calls it “the most important attribute when it comes to providing more metadata for an image”, and notes that it also helps people who use screen readers. Good alt text describes the image plainly in the context of the page. Google warns against “filling alt attributes with keywords”, which “results in a negative user experience and may cause your site to be seen as spam.” For purely decorative images, the W3C’s guidance on decorative images says they should be given a null (empty) alt text, written as alt="", so that screen readers and other assistive technologies can ignore them.
File names count for less than alt text. Google says “the filename can give Google very light clues about the subject matter of the image”, and gives an example: “my-new-black-kitten.jpg is better than IMG00023.JPG.” Renaming is worth doing for new uploads, but it is not the part of the work that carries the most weight.
Context does the rest. Google also draws on the page around the image, including captions and nearby text, so an image placed beside text about the same subject is easier to understand than one dropped into an unrelated page.
Reducing the weight
Modern formats cut file size. Google’s WebP documentation reports that WebP “lossy images are 25-34% smaller than comparable JPEGs at equivalent quality”, with a fallback served to browsers that need an older format. Beyond format, the company compresses files and resizes them to the dimensions actually displayed, and can provide several sizes so phones receive smaller files than large screens.
Two layout details matter for loading speed and stability. Reserving space for each image in the page code stops the page from shifting as images arrive. Lazy loading delays images further down the page until the visitor scrolls toward them, but the main image visible when the page opens should load immediately, because delaying it delays the moment the main content appears.
Agreeing on how image work is found and reported
Ask the company how it will find images that Google cannot see, such as CSS backgrounds, how it writes alt text and handles decorative images, which formats and sizes it will serve, and whether it will set up an image sitemap. Ask too how it will show you the result: lighter pages, and images appearing in Google Images for the searches that matter to you.