Images are an integral part of the vast majority of websites these days and it is important the images you use are both saved in the correct format and optimised as well as possible.

There are predominantly 2 types of graphic used on the internet:-

GIF - used for images with few colours (up to 256)

JPEG - used for images with many colours (photographs, diagrams, shades etc)

The correct use of type and optimisation can make all the difference to your webpage