Sorry for the late reply, I was abroad and internet over there wasn't very good.
The site is https, and so is
https://www.w3schools.com/tags/smiley.gifAnd yes, the block is turned on (the block is visible, the content isn't).
And it can be seen here: (link removed).
(bottom right on the front page, the name of the block is "Test")
If I use an inspector on that block I see that the code there is correct:
<img src="https://www.w3schools.com/tags/smiley.gif" alt="Smiley face" style="height: 2.625em;width: 2.625em;">
I tried it also with an image on the server off the site, still no dice.
Edit: link removed as requested by OP.