HTML/CSS: Advice is to not use pixels to define height/width so that my web site can scale with higher resolution display - however, what do I use to define IMAGE height/width?

Programmer Question

I've read all over the Internet that I should not define fonts (or anything) with absolute pixel height/width/size and instead, use EM ... so that on higher resolution displays, my web site can scale appropriately.

However, what do I use to define IMAGE height/width ... because images won't scale well (they look pixelated)

Find the answer here