For your part, if you intend to create pages to pass around via the interenet, best you observe and learn all the little issues that can ensure the correct and efficient displaying of your pages. Even with a minimum of computer experience you should be aware of folders or directories that reside on the harddrives of the computers you use. They are structured with first level folders containing not only computer program files but perhaps second and further folders within. A server computer, i.e. your ISP might also offer a Hosting Service which allows persons or organisations to store their Internet files and make them available for world wide access. It is usually an expensive exercise, but for just a few pages and images and as a way to learn there are some very good deals around.
Dithers are both a nightmare and a blessing.
We can not easily reproduce a controlled and repeatable infinite variation of tone or density in a truly continuous tone manner. The small solid colours used for web images are laid out in a set pattern - images for the web have to be pixel ised as a controlled mass of the tiny dots. Combined, the mixtures give the illusion of the unobtainable. Look closely and you will find colours missing, replaced by the closest average colour in the reduced Colour Palette . On the right the image appears smoother because a wider range of colours is available.