TL;DR: add http:// to the beginning of the url
So you want to use an image you just uploaded to imgur? Obviously you use the editor, click the image button and paste the url in there, right? But no! Even though the preview looks fine, after you post, the link is dead!
Well, steemit unfortunately doesn't link directly to your image. Instead, it prepends "https://img1.steemit.com/0x0/" to the url. This works in some cases, but I think when the domain name starts with "i" instead of "www" it's broken, and can't follow the link.
What you need to do, is make sure your urls are full urls, with http:// at the beginning, not just the regular url you might find in the address bar of your browser. so just check your urls, if they start with http:// you should be good. Otherwise, paste that in, and that will make sure steemit gets it right.