Why aren't the images loading in Safari when I visit certain websites?

Hey guys. I own a MacBook Pro 13" with OS X El Capitan.

Lately, I've been experiencing some bizarre issues whenever I use Safari.

It turns out that when I visit certain websites, the images associated with those websites just won't load.

An example would be Reverb.com:

https://reverb.com

Whenever I visit that website, none of the images will load, and all of the links would appear as bulleted text.

In addition, I'm having issues with Wikipedia:

https://en.wikipedia.org/wiki/Main_Page

Whenever I visit a Wikipedia article, all of the images would appear as question marks within blue boxes.

And what's funny is that I'm having none of these problems when I visit the Reverb.com and the Wikipedia websites using my iPhone X. All of the images and links load perfectly.

Why do you guys think I'm experiencing all these image-loading problems?

For the record, switching to Chrome still doesn't help.

I'm starting to think that it might be my operating system.

How can I go about resolving these issues?

Thanks guys.