Change img src depending on class

When you use background to set img.

You can change the img by class

<img class=".png" style="background: url('test.png');">

.png{
    background: url('test2.png');
}

However when use src, is it possible to change the img by class?

<img src="test.png">

I think it is possible to change src by javascript, but if I can sort the things by class it is better to handle.

Is it possible?