Img as background-image

Can I make the img tag use the background-image properties? Like for example, I have these two pages here one has img and the other one has background-image tag. Notice in responsive version the img one squeezes the image, while the background-image one adjusts the image according to the size.

• Page with IMG tag


• Page with background-image tag

You can find both img and background-image in sub-header div ..