Some images are huge. Huge images take up lots and lots of space on a web page (both byte-wise and space-wise). By ensuring all images are the smallest possible size, web designers ensure that load times are as fast as they can be. Faster load times mean a better user experience as well as less data transfer usage.
There may not be a one-size-fits-all approach to what “optimize” truly means, there are a few questions to ask when auditing the use of images on your website:
There are so many other considerations that come into play when optimizing images—I’ll provide some excellent resources below—but I cannot stress enough the first point: do not include images for the sake of including images. Images, just like words, should be intentional and should play a part in the overall experience and messaging of any website or digital product.
Optimizing images on your desktop requires the use of a photo editing software. There are many free ones out there and optimizing is just a basic feature. Optimizing involves reducing the file size of an image by either adjusting its pixel dimensions or reducing the resolution altogether.
For images that are going to be viewed on monitors, you can drop the resolution down to 72 pixels/inch, and still get a sharp image on your screen. File size can also be reduced by adjusting the pixel dimensions. A good image size for most images is 500 pixels wide with the height adjusted to proportion of the width.
Google has a more detailed guide on this.