how? Calling the source in the
<img> like this:
It got transformed from the original file which was 6000px wide!
Now, on the server, there is a cached version of this transformed image. There is no need to do the transformation again next time someone requests this image.
The best of all is that you get Moz-jpeg compression by default on all your JPEGs.
You can do many different transformations to you images, like: quality, face-crop, face-blur, width, height, crop, background, rotate, scale, amongst many others.