<img src="img/100x100.png">
<img src="img/200x200.png">
<img src="img/200x200.png" width="100">
<img src="img/100x100.png" srcset="img/100x100.png, img/200x200.png 2x">
<img src="img/100x100_a.png" srcset="img/100x100_a.png, img/200x200_a.png 2x">