I notice there are a lot of photos that dont fill the screen, is this because they have chosen to do this or is it because their camera cant produce images to fill the screen. I noticed my Canon G6 fits the width of my 17" monitor but it stretches virticaly slightly when i set it to desktop. Can i adjust this ?

Please forgive me i am very new to photography and i would read the manual but i had to return my camera because of a minor problem.

Basically this has to do with the resolution of the image. As a norm most people have a desktop resolution of 1024x768 on a 17" monitor. Although it could also be 1280x1240. So you need to download the image that fits your monitor's resolution best.

braveheart is also talking about having an image which is a different aspect ratio (length/width). In general you won't get an image with an aspect ratio different from your monitor to fill the screen. There will have to be some cropping or non-square stretching.