<div style="background: #ccc; width: 40em;">
<img style="width: 100%; max-width: 800px;" src="pics/pattersonsCurse789.jpg" alt="">
See how the pic grows to about the maximum of its native size of 789px on user text size increases. And shrinks to whatever is the width of its grey container when the latter gets less wide than the native width of the picture. Change the text size (under Zoom Text Only) of your browser to see this.