The short answer
Most business sites are slow because of images. Resizing to the size actually displayed and compressing properly usually takes the largest single chunk out of page weight, and free tools do all of it.
Then check the licence on anything you did not make yourself, because free to download is not the same as free to use commercially.
The optimisation that matters
- Resize to the largest size the image is actually displayed at, plus a margin for high-density screens.
- Compress, checking the result visually rather than trusting a number.
- Use a modern format with a fallback for older browsers.
- Serve different sizes for different screen widths.
- Load images below the fold lazily.
Step one is the most commonly skipped and the largest saving. A photograph straight from a camera displayed at a few hundred pixels wide is carrying many times the data it needs.
Licensing is the risk
| Source | Check |
|---|---|
| Free stock sites | Commercial use permitted, attribution required? |
| Icon sets | Licence often requires attribution |
| Fonts | Web use and commercial use are separate permissions |
| Search results | Never assume, most are protected |
| Generated images | Provider terms vary on commercial use |
The fourth row causes real problems. Images taken from search results are a common and expensive mistake, and rights holders do pursue it.
Keep a record
Note where each image came from and under what licence, in a file alongside the assets. It takes seconds at the time and is close to impossible to reconstruct two years later.
That record is what you need if anyone ever asks, and it also makes it possible to replace an asset when a licence changes.
Do not over-engineer it
For a business site, a handful of well-chosen, properly sized photographs beats a large library. Every image is weight, and most decorative ones earn nothing.
Where an image is purely decorative, consider whether the page is better without it. That is frequently the fastest optimisation available.