We’re always coming across websites where some of the images take longer to download than others. This is usually because they are disproportionally large compared with the area reserved for them on the site.
Whereas once, a web developer would optimise images to suit websites during the build, modern widespread use of content management systems allows anyone to upload images practically directly from a camera.
The downside to this is that the website is less than efficient, particularly for those with slower broadband speeds. It also means that your images are more likely to be downloaded and used on other sites.
Best practice is to optimise them first, using a programme like Preview (Mac) or Microsoft Picture Manager (Windows). You should be looking for the ‘Adjust Size’ tool, to reduce not by a random percentage, but to an exact size. 200 pixels wide (landscape) is a good size for a small image or a gallery preview. A feature image should be 400 – 500 pixels wide (landscape). This is still significantly smaller than Flickr, but it’s enough detail for most websites.
It’s easy to work out if your images are too large – saving them to the desktop will force them to appear at their actual size when opened. If they’re larger when opened from the desktop than they appear on your website then resize them.
Equally, images should not be stretched if they are too small – otherwise there’s a loss of quality.