For those with a strong desire to use `<picture>` but also want to support legacy browsers, there's (almost) always a polyfill.

In this case: https://scottjehl.github.io/picturefill/

Isn’t it why you still put an img element in it ? Or am I mistaking ?

True, of course then you will have to deal with the formating problems that made you choose background-image over img in the first place. Though concidering the small numbers still using IE 11 that might be acceptable.