Hello, can anyone advice me with the following please

My website Im designing has approximately 100 pages and at the moment each page has its own folder to store that pages images i.e. pageone.htm has directory pageone_files and pagetwo.htm has pagetwo_files etc.

I was thinking..... is this the best way to have the structure bearing in mind about 80% of the images are common through out my site, or should I have just one directory storing all images therefore dramatically reducing the size (bytes) of my site.
Also if using just one directory will there be a speed issue making the site load slower?
Thanks all in advance
sanc