When you go directly to the URL of an image on your web server in a browser (such as the URLs you posted above), you are taking Juicebox out of the equation. If the browser cannot load the image, then the problem is likely to be one of three things:
(1) a web server problem
(2) an internet connection problem
(3) a problem with the image itself on the server

As I can see the problem for myself (your 'dragon.jpg' image is only 515KB but took over a minute to load), we can rule out your internet connection as being the problem.

Also, as the image did eventually load without errors, it looks like there is no problem with the actual image file on your server (it does not appear to be corrupt).

This leaves the web server itself as the most likely cause of the problem.

I would contact your web host and ask them if they are currently experiencing any issues which might be contributing to your problem. Also, ask them directly why your images are taking so long to load. They should hopefully be able to help further.

The ERR_CONTENT_LENGTH_MISMATCH message you are getting might be due to the fact that your browser is timing out whilst trying to load the image (rather than suggesting that there is a problem with the image itself).

Incidentally, if I try to go to what I expect might be your home page (http://www.kleibography.com), I get the following message:

This message looks to have been generated by Wordfence firewall.
I don't know if the two issues are related but you could try temporarily disabling your Wordfence firewall to see if this makes a difference.