Images need to be adjusted and optimized before they are entered on a page, 
so that they load quickly. Pictures are not part of the page. They must be store with the .html files so that a link can be formed to load them on to the page when browsed. A picture can say a thousand words. 
.jpeg files are used for photographs.(Also .bitmap) 
.gif files are used for animations and graphics.(Only .gif allows transparency) 
 

Animations add life to page.