1. A medium image contained in a paragraph with no styles applied

#img1 {}

2. A medium image with a width of 100% (no height set)

#img2 IMG {width:100%;}

3. A medium image with a width of 100% and a max-width equal to the actual image size (no height set)

#img3 IMG {width:100%; max-width:320px;}

4. A medium image with a max-width of 100% (no height or width set)

#img4 IMG {max-width:100%;}

5. A medium image with a max-width of 100% and a width equal to the actual image size (no height set)

#img5 IMG {max-width:100%; width:320px}