Forum Moderators: mack
Do you have any examples of any such sites? There are ways to resize images in that way but I don't think I've ever seen it done as a general fit-to-screen approach. Browsers tend to do so pretty sloppily.
The only times I've ever seen it done were for accessibility issues (resizing the page for ease of reading). It could be possible that there are alternate versions depending on resolutions, but even that may be rare.