Browser will show the image on its real size and you can change that (not needing to have an image for each size) with the CSS style attributes:
<img src="image.bmp"> <!--this is the normal size-->
<img src="image.bmp" style="width:100%"> <!--this is the 100% of the screen-->
<img src="image.bmp" style="width: 30px"> <!--this is going to resize the image to 30px wide-->
<!--you can do the same with the height attribute, but you are
encouraged to not use both at the same time so you can keep the ratio-->