Hi, If a visitor comes to my website and it has one 100kb image on it, it will use 100kb bandwith right? But what if the same user comes back the next day, will it use 200kb then? Or only 100kb because of Temporary Internet Files?
Really just depends on client-side caching, which you can't really depend on. Best to consider a worst-case scenario. In that case, yes the 100KB image would be downloaded each time the visitor goes to your website.
Hi, Don't forget that if you have a html page with a bunch of images on it the total amount it will download is the html plus all the images (and CSS, Javascript files, etc). Most browsers implement some caching but it is best not to count on it.
To make it more complex still, your page - or parts of it - could be cached on the users ISP or somewhere else along the way. Some users might be using accelerator software or services which deliberately cache pages etc etc. These will reduce bandwidth used on your server. Any user who hits Ctrl+F5 (Firefox or IE) several times will load the page and images from your server several times regardless of cached copies available.