Almost all sites will contain graphics, these can be layouts, diagrams, logos, banners, illustrations or photographs.
Layout graphics are the graphics that give the site its 'looks'. They might include page titles and buttons.
Photographs are often used on web pages. Photographs can be taken using a digital camera or scanned from prints or negatives.
Flash can be used for graphic elements within a site such as a banner or animation.
These are moving images, used for banners or page elements.