Google sees things differently than we do. You look at a photo of a golden retriever in a raincoat and see a "good boy" staying dry, but a crawler sees a cluster of pixels, a file name like IMG_567.jpg, and maybe a few bytes of metadata. If you want that photo to show up in a search or, better yet, land on a user's Google Discover feed, you have to bridge that gap. Learning how to label an image isn't just about accessibility—though that’s huge—it’s about giving a search engine the "why" behind the "what."
Honestly, most people mess this up. They stuff keywords like it’s 2005 or they leave the alt text blank because they're in a rush. That's a mistake.
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The Alt Text Trap Most People Fall Into
Alt text is the heavy lifter. It’s the text that appears if an image fails to load and, more importantly, it's what screen readers announce to visually impaired users. Google uses it as a primary signal for understanding image context.
But here is the thing: context is everything. If you have a picture of a laptop on a wooden desk, and your article is about "remote work ergonomics," your label should mention the posture or the desk setup. If the article is about "minimalist interior design," the label should focus on the wood grain and the aesthetic. Don't just say "laptop on desk." That's lazy. It tells the bot nothing about why this specific image belongs in this specific story.
Google’s own John Mueller has mentioned time and again that alt text should be descriptive and natural. Think about how you’d describe the photo to a friend over the phone. You wouldn't say "keyword-laptop-office-setup-best-prices." You’d say, "A silver laptop sitting on a reclaimed oak desk with a small succulent next to it."
Why File Names Are Your Secret Weapon
You've probably seen images on websites with names like final-final-v2-edit.png. That is a wasted opportunity.
Before you even upload a file to your CMS, you need to change the name. Use hyphens. Not underscores. Google’s algorithms are historically better at reading hyphens as word separators. So, how-to-label-an-image.jpg is readable; how_to_label_an_image.jpg is a bit of a gamble.
Keep it concise. You don't need a paragraph in the file name. Stick to four or five words that define the subject. If it's a product, include the model number or the color. Detail matters here because it creates a breadcrumb trail for the crawler to follow from the file system all the way to the rendered page.
Structured Data and the Discover Feed
Google Discover is the holy grail for traffic right now. It's that feed of articles on your mobile phone that seems to know exactly what you’re interested in. To get an image there, you need more than just a good label; you need high resolution.
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Google’s documentation specifically recommends that images for Discover be at least 1200 pixels wide. But there's a technical side to how to label an image for these high-visibility spots: Schema markup.
Using ImageObject schema tells Google, "Hey, this isn't just a random decoration; this is a primary asset of this content." You can specify the license, the creator, and the caption within the JSON-LD code. This is particularly vital for news organizations and bloggers who want their images to appear with that "Licensable" badge in Google Images, which can actually improve click-through rates because it signals professional-grade content.
Captions: The Part You Shouldn't Skip
People read captions. Studies from the Poynter Institute on eye-tracking show that captions are some of the most-read bits of text on a page. While alt text is for the bots and accessibility, captions are for the humans.
A great caption adds information that isn't obvious just by looking at the photo. Don't just describe the image—enhance it. If the image shows a graph of rising inflation, the caption shouldn't just say "Inflation graph." It should say "Inflation reached a 40-year high in June 2022, driven largely by energy costs."
This creates "semantic closeness." When the text surrounding an image—including the caption—is highly relevant to the image itself, Google gains more confidence in what that image represents. It strengthens the topical authority of the entire page.
The Technical Stuff: Formats and Compression
Let’s talk about WebP. If you're still using massive JPEGs or transparent PNGs for every single thing, you're slowing down your site. Site speed is a ranking factor.
WebP is the format Google loves. It provides superior lossless and lossy compression. You can have a beautiful, crisp image that’s 30% smaller than its JPEG counterpart. When you label these images, make sure you aren't sacrificing quality for speed or vice versa. Use "lazy loading" so the images only load as the user scrolls down. This keeps the initial page load fast, which keeps Google happy.
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What to Avoid (The "Don'ts")
- Don't use "Image of" or "Photo of": Google already knows it's an image. You’re just wasting space.
- Don't keyword stuff: If your alt text is "dog, puppy, golden retriever, pet, cute dog, dog for sale," Google might flag it as spam.
- Don't label decorative images: If an image is just a decorative line or a background shape, leave the alt attribute empty (
alt=""). This tells screen readers to skip it so they don't annoy the user with "thin blue line" every five seconds. - Don't ignore the context: A picture of a hammer on a carpentry site needs a different label than a picture of a hammer on a legal blog discussing "bringing the hammer down."
Actionable Steps for Better Image Optimization
First, audit your most popular pages. Look at the images that are already driving some traffic and see if their alt text is actually descriptive or just a placeholder.
Next, implement a naming convention for your team or yourself. Every single file should follow the primary-keyword-description.extension format. It takes five extra seconds but pays off in long-term SEO equity.
Third, check your "Large Image Summary" in your meta tags. For Google Discover, you want to ensure your site is signaling that it has high-quality assets available. Use the max-image-preview:large meta tag in the header of your pages. This tells Google it's okay to show your high-res image in the Discover feed, which is often the difference between a tiny thumbnail and a massive, clickable card.
Finally, verify everything in Google Search Console. Look at the "Performance" tab and filter by "Image." You can see exactly which queries are bringing people to your site via image search. If you see a weird query ranking for one of your photos, go back and tweak the labels to better align with what people are actually searching for. SEO is never "one and done." It's a constant process of refining how you describe your world to the machines that index it.