Image SEO Best Practices: Alt Text, Compression, and File Naming

You’ve written a great piece, the kind that should get shared, saved, and searched for. Then the page loads, and the images take their time, or don’t show at all. Worse, Google Images ignores them, even though they’re the best part of the story.

That’s the quiet frustration of image SEO. It’s not mystical, and it’s not just for developers. Most wins come from three things you can fix today: alt text that says what the image actually shows, files that load quickly without looking rough, and file names that make sense to humans and search engines.

Get these right and you’ll often see faster pages, better accessibility, and more chances to appear in image search results. In January 2026, that’s not “nice to have”, it’s basic hygiene for publishing.

Alt text that helps people and helps Google

Alt text (short for alternative text) is the written description attached to an image in your page’s code. It shows up when an image can’t load, and it’s read out by screen readers for people who can’t see the image.

It also gives search engines a plain-language clue about what the image contains. Google has been clear that image understanding comes from context, not guesswork, and alt text is part of that context (alongside captions, surrounding copy, and page structure). Their own guidance is worth keeping bookmarked: Google image SEO best practices.

Think of alt text as a promise: “If you can’t see this, here’s what you missed.” When you write it with that mindset, you usually make it better for rankings too.

Write alt text like you are describing the image over the phone

If you had to describe the image to a friend who can’t see your screen, what would you say in one breath? That’s the tone you want. Useful, calm, and specific.

A simple formula that works on almost any page:

Subject, action, setting (only what matters).

• Subject: who or what is in the image?
• Action: what are they doing, or what is happening?
• Setting: where is it, if the place adds meaning?

Keep it short. A good practical target is under 125 characters, because many screen readers cut off long descriptions. If a key phrase fits naturally, include it, but only if it matches the scene. If you wouldn’t say it out loud, don’t force it into the alt text.

Examples of “phone description” style alt text:

• “Reporter taking notes in a crowded council meeting”
• “Line chart showing UK inflation falling from May to October 2025”
• “Cup of flat white beside a laptop on a café table”

If the image contains text that matters (a chart label, a quote in a screenshot), include the essential meaning in the alt text. Don’t try to reproduce every word; capture what the reader needs to know.

For a deeper checklist-style approach, this UK-focused guide is handy: The Definitive Guide to Image SEO & Alt Text Best Practices.

Alt text mistakes that hurt trust (and rankings)

Alt text can also backfire when it reads like a billboard. Search engines don’t “reward” awkward stuffing, and users who rely on screen readers feel the pain right away.

Common mistakes to avoid:

Keyword stuffing: repeating the same phrase, or cramming in variants that aren’t visible in the image.
Copy-paste alt text: using identical alt text across a gallery of different images.
Starting with “image of” or “picture of”: screen readers already announce it’s an image, so you’re wasting space.
Leaving alt text blank on important images: if the image carries meaning, blank alt text removes that meaning for some readers.

There is one exception that’s worth knowing. Decorative images (pure styling, separators, background flourishes) can have empty alt text so screen readers skip them. That keeps the experience clean. The trick is to be honest about what’s decorative and what’s informative.

Bad vs better examples (quick and real):

1. Bad: “Image of SEO image optimisation best practices alt text compression file naming”
   Better: “Screenshot of PageSpeed Insights showing image warnings and load time”

2. Bad: “Laptop, laptop on desk, laptop desk SEO”
   Better: “Editor reviewing a draft article on a laptop at a wooden desk”

3. Bad: “IMG_1044” (yes, people do this in CMS alt fields)
   Better: “Before-and-after photo of a compressed hero image, same quality, smaller file”

If you want a broader overview that ties alt text into on-page SEO, this guide is a solid reference: Image SEO: Alt Text, File Names, and Compression Guide.

Image compression and modern formats, faster pages without ugly blur

A slow-loading page feels like a shop with a sticky door. People still get in, but fewer will browse, and fewer will come back. Images are often the reason.

Compression is simply reducing file size while keeping the picture looking right. Smaller images load faster, scroll smoother on mobile, and put less strain on data plans. That can improve user behaviour signals (less bouncing, more reading) and performance metrics that search engines care about.

In 2026, the practical takeaway is simple: use modern formats when you can, and compress with intent. WebP and AVIF often deliver the same visual quality at a smaller size than JPEG or PNG, which is why they’re now widely recommended for web publishing (including in mainstream SEO guidance such as 15 Image SEO Best Practices).

Choose the right format: JPEG, PNG, WebP, or AVIF

You don’t need to memorise specs. Match the format to what you’re publishing.

JPEG
Best for photos when you need wide compatibility and quick exports. It compresses well, but it can show artefacts if pushed too far.

PNG
Best for graphics with sharp edges, text overlays, and transparency (like logos). The files can be heavy, so don’t use PNG for large photos unless you have a reason.

WebP
A strong all-rounder for web publishing. It often shrinks file size a lot without visible quality loss. Many CMS platforms and image plugins can auto-serve WebP versions.

AVIF
Often the smallest for the same quality, especially on photos. It can be great for hero images and large visuals, as long as your setup serves fallbacks when needed (many modern tools handle this automatically).

A simple rule that avoids most mistakes:

• Photos: start with WebP (or AVIF if your system supports it well), fall back to JPEG if needed.
• Logos, icons, and graphics with transparency: PNG or WebP.
• High-impact hero images: test AVIF against WebP and keep the one that looks best at the smallest size.

If you’re working inside a CMS, check whether it can convert on upload or serve next-gen formats automatically. It saves time and reduces human error.

A simple compression workflow you can repeat every time

Compression only works if you handle sizing first. Uploading a 4000px-wide photo and “letting the theme resize it” usually means you’re still shipping a large file, just displayed smaller.

Here’s a repeatable workflow that fits into everyday publishing:

1) Set sensible dimensions before upload
Know where the image will appear. If your article content area displays images at 800px wide, exporting at 1600px gives some sharpness for high-density screens, without going overboard.

2) Compress with a realistic quality target
If your tool has a quality slider, 70 to 80 percent is a common sweet spot for most blog images on mobile. Then check it with your eyes. Faces, text, and fine lines show compression problems first.

3) Zoom to 100 percent and inspect the trouble spots
Look at edges, skin tones, gradients (like skies), and any text inside the image. If it looks crunchy or smeared, step the quality up a little.

4) Keep an eye on file size, not just quality
There’s no magic number, but many publishers aim to keep typical in-article images comfortably small. If a single image is huge, it needs attention.

5) Use lazy loading for below-the-fold images
Lazy loading means images load as the user scrolls, not all at once. It can reduce initial load time and make the page feel quicker, especially on mobile connections.

6) Test with PageSpeed Insights after changes
Don’t guess. Run the URL through Google’s tool and see what it reports: Google PageSpeed Insights. It will often point straight at oversized images and next-gen format opportunities.

If you’d like a plain-English guide that ties compression back to SEO outcomes, this is a good read: How to Optimise Images for SEO.

File naming and placement, make your images easy to understand

Search engines don’t just “look” at pixels. They read the story around the image. File names, captions, headings, and the paragraph beside the image all help confirm what it is.

A clear file name won’t rescue a weak page, but it does remove friction. It’s like labelling a folder before you put it in a drawer. When you need it later, you’ll find it faster, and so will Google.

SEO-friendly file names: clear, short, and spaced with hyphens

File naming best practice is simple, and that’s why it’s often ignored.

Use these rules:

• Use real words that describe the image.
• Use hyphens between words (search engines treat hyphens as separators).
• Avoid underscores and spaces.
• Keep it short and readable.
• Match what’s actually in the image.
• Rename camera defaults like IMG_0041.jpg before upload.

Four examples you can copy as a pattern:

• Product-style: black-leather-chelsea-boots-side-view.webp
• News-style: london-mayor-press-conference-january-2026.jpg
• Chart-style: uk-inflation-rate-line-chart-2025.png
• Person-style: data-analyst-working-at-desk.jpg

If your content team is busy, this is an easy habit to build: rename the file at the same moment you export it. It takes ten seconds and saves months of “what on earth is IMG_8392?”

Context signals that strengthen image SEO (without extra work)

Once the file name is sensible, the next wins are about placement and meaning.

Put images near the matching paragraph
If the image supports a point, place it beside that point. When you scatter images far from their related text, you weaken the context.

Use captions when they add information
A caption isn’t mandatory, but it can help when the image needs interpretation, like a chart, map, or on-the-ground photo. Keep captions factual, not cute.

Keep one idea per image
If you cram three concepts into one graphic, your alt text becomes long and messy, and the reader doesn’t know where to focus.

Use responsive images so they look right on mobile
Responsive images (often handled by your theme or CMS) serve different sizes based on the device. That reduces wasted bytes and keeps layouts tidy.

Help discovery for key images
For larger sites, consider including important images in an image sitemap so search engines can find them. For certain content types, structured data can also help clarify what the image represents (products, recipes, and articles are common examples). Keep it simple and only add markup that matches the page content.

Conclusion

Image SEO doesn’t need a big re-build. It’s mostly a set of small choices that stack up. Write alt text that sounds like a calm description, not a list of keywords. Compress images so pages load fast, and prefer modern formats like WebP or AVIF when your setup supports them. Name files like a human would, with hyphens and clear words.

If you’ve got 15 minutes, pick one post and do a quick clean-up: rename the top three images, tighten the alt text, compress any heavy files, then check the page in PageSpeed Insights. Once you see the difference, you’ll want to make it part of your publishing routine.