It is because proxy ban from imgur.com months ago.

You can pull your request to imgur.com and wait for their policy change but I think it will be hard to convince them to change policy.

Meanwhile, you can go to those thread, click on quote and get image links on imgur.com, copy, paste it on the browser to see those images.

You can use this script

• If you have problems with images that were uploaded by imgur.com, let's check scripts
  
  • [Script] Imgur to TalkImg - automatically fix your broken images
  • [Script] Fix broken Imgur images forum-wide (client only)

Image uploading websites/ scripts for Bitcointalk users[/img] has some alternative websites for image upload.[/list]