How to Fix a Slow Website: Image Issues That Make Your Site Heavy
In this second part of the series, we look at how to spot them, understand them, and fix them in a practical, human way — using only your browser.
Thu Nov 13 2025 • 5 min read
This article is part of a series about fixing slow websites using nothing more than your browser. In the first part, we looked at how to diagnose performance issues: reading the waterfall, watching what the browser does behind the scenes, and spotting the first clues. If you missed it, you can find it here:
👉 Diagnose Problems Using Your Browser
Now that you know how to see your site’s behavior clearly, let’s focus on the most common reason pages feel slow: images.
I’ve lost count of how many times a client has told me “our site feels heavy,” only for the browser to reveal a single 4 MB hero image dragging everything down. It’s almost always the same story: great-looking images saved in a way the browser struggles with.
This part of the series is about understanding why that happens and how to fix it — gently, simply, without needing to become an image expert.
Why Images Slow Down Websites So Easily
If you think about it, images are the only part of a webpage that arrive with “baggage.” Text is tiny. CSS is tiny. Even JavaScript, when optimized, is reasonable.
Images, on the other hand, carry megabytes of information just to show a few colors on the screen.
The trouble begins when those images are bigger, heavier, or more detailed than the page needs. A browser is patient, but when you ask it to decode a 4000-pixel-wide photo for a section that displays at 380 pixels, it does what you ask — and you feel the cost.
How to Spot Overweight Images
Instead of jumping into tools or theory, start with your own eyes.
Open your site in an incognito window. Bring up DevTools, switch to Network, and reload.
You’ll see a flood of requests slide in. Focus on the “Size” column.
If the top items in the list are image files, and they’re measured in megabytes rather than kilobytes, you’ve already uncovered most of the story.
A fast website doesn’t need tiny images — it needs appropriate ones.
What Really Makes an Image Heavy
It’s tempting to think the file size is the whole issue, but there are three forces at play: dimensions, format, and compression. Once you understand these, everything else becomes simpler.
Dimensions (how big the image really is)
Imagine printing a poster and then displaying it as a thumbnail. That’s what many websites do. The browser politely shrinks massive images down, but it still has to process the entire file.
If your image is displayed at 400px wide but the actual file is 4000px, you’ve multiplied the browser’s work for no benefit.
Format (how the image stores information)
JPG, PNG, WebP, AVIF — these aren’t interchangeable.
- JPG excels at photographs.
- PNG is crisp for text and UI, but enormous for photos.
- WebP is often smaller than JPG, without visible loss.
- AVIF is the smallest, though slower to encode.
If your large homepage banner is a PNG, it’s wearing a winter coat in summer.
Compression (how the details are packed)
A JPG saved at 100% quality is unnecessary almost everywhere. Dropping it to 80–85% produces a file dramatically smaller, with a difference no visitor will ever notice.
These three elements decide whether your images feel light or heavy — not mysterious optimization tricks.
A Quick Check Inside DevTools
Click any image in the Network panel. Scroll through the details. You’ll see something surprisingly helpful: the actual dimensions of the file and the rendered size on the page.
If the browser says:
- Rendered: 380×250
- Actual: 4032×3024
…you’ve just found a perfect example of wasted weight.
A browser can handle it, but why make it? Most of that data never reaches the screen.
Serving Only What Each Device Needs
One of the most silent causes of slowness is serving the same large image to every device: desktop, tablet, phone.
If a 2000px image is sent to a small phone, you’ve just burned most of the visitor’s budget for no gain.
Responsive images (srcset) let the browser pick the right size automatically. You don’t need to memorize the syntax to use it — just provide smaller versions whenever your platform or CMS allows it.
A phone deserves a lighter file. A laptop deserves a medium one. A 4K screen can handle the big version.
Let the browser choose.
Lazy Loading as a Gentle Optimization
Think about what the visitor sees first. If the image is below the fold, it doesn’t need to be fetched immediately.
Adding loading="lazy" is a small instruction that tells the browser: “Wait until the visitor scrolls.”
It keeps the initial load light and focused.
Fixing Images Using Local Browser Tools
The nice thing about images is that you can fix almost everything before uploading anything. That makes them ideal for browser-based tools — fast, private, and easy.
On Vayce, you can:
- Compress an image without hurting clarity.
- Convert a large JPG to a lighter WebP.
- Resize an image to match its real display size.
- Crop out unnecessary areas.
Once you optimize an image once, it stays optimized. And your site immediately feels lighter.
Closing Thoughts
Images are the most common source of slowness not because they’re complex, but because they’re often forgotten. But once you know how to spot oversized files, understand what makes them heavy, and adjust them properly, you remove one of the biggest barriers to a fast, smooth site.
In the next part of this series, we’ll look at another familiar cause of sluggish pages: JavaScript and third-party scripts — the silent blockers that affect speed even when your images are perfect.
