To reference an external image and make sure it appears with a controllable parameter, one can reference this page on Stack overflow^[1].

The original post by stack overflow user Brion is reproduced and the template has been created here:

The first step is to add one more line in LocalSettings.php.

$wgAllowExternalImages = true;

Then, you need to have admin access to the MediaWiki site, so that you can edit the file:MediaWiki:Common.css.

.externalimage-holder {
    position: relative;
}
.externalimage-holder img {
    width: 100%;
    height: auto;
}

Then, set up a Template in Template:Sized-external-image like this:

<div class="externalimage-holder" style="width:{{{1}}}">{{{2}}}</div>

Then, call it like this:

{{sized-external-image|250px|https://storage.cloud.google.com/pub_papers/GitiFactory.png}}

Then, it should show up as follows:

References

External Image