Image SEO: What Actually Affects Your Google Rankings

Search for advice on image SEO and you will hit a wall of confident numbers. Filenames are worth “15 to 20% of the ranking signal”. Renaming your images gets you a “40% traffic increase”. Most of these do not trace back anywhere. No study, no methodology, no source, just a figure precise enough to sound researched.

Below is only what we could verify, from Google’s own documentation and its search advocates on the record. It is a shorter list than the hype suggests, and it ends somewhere most image SEO advice never goes. The one factor with hard numbers behind it is not the filename. It is not the alt text either. It is how much your images weigh.

How Google reads your images

Google’s Search Central documentation is direct about what it uses to understand an image: the filename, the alt text, the surrounding page content, and computer vision analysis of the image itself. None of these works alone. Google says it uses alt text “along with computer vision algorithms and the contents of the page to understand the subject matter of the image”.

That combination matters more than any single field. A well-worded filename on a page with no relevant surrounding text is a weaker signal than an unremarkable filename on a page that is clearly about the subject of the photo.

Filenames: what helps

Google’s guidance is refreshingly plain: use filenames that are short but descriptive. Their example is my-new-black-kitten.jpg rather than IMG00023.JPG. That is not a keyword exercise. It is naming the thing in the photograph.

What works:

• Describe what is in the image: navy-canvas-backpack-front-view.jpg, not product1.jpg
• Separate words with hyphens
• Keep it readable. Someone should be able to guess what the image shows from the filename alone
• Match the filename to what the page is about, not to a keyword you wish it ranked for

What does not help, and can backfire:

• Stuffing filenames with variations, like backpack-buy-backpack-cheap-backpack-online.jpg
• Renaming every image to the same head term. It stops being descriptive and becomes noise
• Treating the filename as a substitute for good alt text or page content

There is no verified evidence that filenames carry a fixed percentage of ranking weight. What is verifiable is that a descriptive filename is one more consistent signal helping Google, and anyone scanning image results, understand what they are looking at.

Alt text: useful, but not the lever people think

This one is worth being precise about, because it is the most overhyped. In a Google Search Central office-hours hangout on 18 March 2022, John Mueller said “the alt text really helps us to understand the image better for image search”, and was explicit about the limit: “It’s not that the webpage in the text web search would rank better because it has an image.” He clarified on 26 March that Google does treat alt text as part of the page, searchable and able to appear in a snippet, but that “the primary purpose however is for images”.

Worth noting how hard that was to pin down. The same sentiment circulates attributed to 2020, 2021 and 2023 depending on which article you read. The dates above are the ones with a named venue attached.

In practice:

• Write it for the person who cannot see the image, first. Describe what is there and why it is relevant on this page
• Be concise and specific. “Dalmatian puppy playing fetch in a park” beats both “dog” and a string of keywords
• Do not leave it blank on meaningful images, and do not stuff it. Google warns that keyword-stuffed alt attributes “may cause your site to be seen as spam”
• Purely decorative images can use an empty alt="". You do not owe every image a paragraph

If you take one thing from this section: alt text is an accessibility requirement first and an image search signal second. Treating it as a keyword density game is the fastest route to alt text that helps nobody.

One thing has changed since this was written, and it raises the stakes rather than altering the advice. The systems reading your alt text now include multimodal models assembling an answer, not only a crawler building an index, and they read it alongside the pixels, the filename and the paragraph around it. What AI search changed, and what it did not goes through the evidence. The short version is that a plain, accurate description is worth more than it used to be, to more readers than before, and that some of those readers are machines writing about you.

The factor nobody puts in the headline: file size

Images are the heaviest thing on almost every page. The 2025 Web Almanac, built by HTTP Archive from real crawl data, puts the median home page at 1,058 KB of images on desktop and 911 KB on mobile. More than JavaScript. More than fonts. More than anything else on the page, and about half of its total weight.

This is the part most image SEO articles skip, and it is the part with the least ambiguous evidence behind it.

Google puts it plainly in its own guidance: “images are often the largest contributor to overall page size, which can make pages slow and expensive to load”. A page full of oversized images is slower for every visitor on every device.

The fix is boring and effective:

• Resize before uploading. A 4,000px photo displayed at 800px is five times the data for no visible benefit
• Use modern formats. WebP and AVIF produce smaller files at equivalent quality, and Google Search supports both
• Compress. Most images tolerate real compression before the loss becomes visible
• Strip metadata you do not need. EXIF and location data add weight, and on user-submitted photos can leak information you never meant to publish

A workflow, not just a checklist

Teams do not fail at image SEO because they do not know the rules above. They fail because applying them to 40 product photos, one file at a time, is boring enough to skip when a deadline is close. Simple in theory, quietly never done.

That is the specific problem worth solving with a batch process rather than willpower: take the set of images you are about to publish, generate descriptive filenames and alt text for the whole batch, resize and convert to the format you need, and strip metadata, before a single file reaches your CMS.

That is what we built Resiqo around. Resizing, conversion and packaging run in your browser, so your full-size originals never leave your device, and every suggested name is editable before you export. The free plan covers 20 named images a month; resizing, conversion and export are unlimited for everyone.

Whether you use a tool or do it by hand, the point stands. The biggest image SEO win most sites are leaving on the table is not a clever trick. It is doing the basics consistently, on every image, rather than on the ones someone remembered to fix.

A short, honest checklist

• Filename describes what is in the image, in plain words, hyphen separated
• Alt text describes the image for someone who cannot see it
• Image is resized to the dimensions it is displayed at
• File is compressed and, where practical, served as WebP or AVIF
• Image sits near text genuinely relevant to it
• Unnecessary metadata is stripped before publishing
• For key product or editorial images, consider ImageObject structured data if you want eligibility for image rich results

Questions people ask

Does renaming old images move the needle?

There is no reliable data showing a guaranteed lift from renaming existing images, and changing the URL of an already-indexed image needs redirects. It is more defensible to get filenames and alt text right on new content, and fix old images opportunistically when you are already updating that page.

Do I need alt text on every image?

Every meaningful image, yes. Purely decorative ones can use alt="" so screen readers skip them. That is the documented accessible approach, not a gap.

Is WebP better than JPEG for SEO?

WebP usually produces smaller files at similar quality, which helps page speed. That is an indirect but real benefit, not a format-specific ranking bonus.

How long until changes show up?

Google has to recrawl and reprocess the page, which takes days to weeks depending on how often your site is crawled. There is no fixed timeline, and any specific number of weeks is exactly the sort of unsourced claim this article is trying to avoid.

Sources: Google Search Central, Image SEO best practices; Search Engine Journal, Google: Alt Text Only A Factor For Image Search; HTTP Archive, 2025 Web Almanac: Page Weight. Every quotation and figure above was checked against these sources before publishing.