• jpg (jpeg)
• gif
• png

The last one – png is a fairly new standard and is still not fully supported by older browsers. If you don’t care that older browsers won’t see it then you may want to risk it and use png for your site.

However the other two options (jpg and gif) have been viewable in browsers for a very long time.

In general jpg is better for photos and images with lots of gradients and fancy stuff in, whereas gif is better for images created on a computer out of shapes. These days most of the time you will end up using jpg but its up to you.

jpg is a lossy format which means that you lose information in an effort to try and make the image small. I’m not going to bother with details here but if you look carefully at a highly compressed jpg image you will notice the places where the information has been removed to make the file smaller.

Again, as a rule of thumb, you should be compressing your images down to about 75% or above – anything lower and the image starts to show its compression. It does depend a lot on the image and what detail and colours are in it but you can often see a preview of the image as you compress it in your software. If in doubt go bigger rather than smaller.

Why bother compressing at all?

Well the smaller the image the faster it will load in the browser and fast is always a good thing on the Internet.