Let's go over it step by step. I'm going to have to make some guesses since your problem description is extremely non-specific. If at any point I'm mistaken, simply provide a clear guide to reproduce your issue.
I've uploaded an image to imgur. Here's a link to the album:
https://imgur.com/a/fNSg3hsIt is my assumption that your final product looked something along the lines of
[img]https://imgur.com/a/fNSg3hs[/img] or
[img]https://imgur.com/bIRhQJv[/img], neither of which would work.
What you need to do is use the URL of the actual image
file - in my case that would be
https://i.imgur.com/bIRhQJv.jpg. You can obtain it in a number of ways, but here are a couple of quick examples:
Option 1: [Should work for most websites]. Right-click on the image and find the "Copy image address" (Chrome) or "Copy Image Location" (Firefox) option. Different browsers may use slightly different names, but it should be within the realm of the obvious now that you know what you're looking for. The correct URL is now in your clipboard.
Option 2: [Specifically for imgur, for any image you personally uploaded] When you mouseover the image you've just uploaded. You should see a small context menu in the top right corner.
Navigate to the "Get share links" option, and copy the "BBCode (Forums)" option. Note that this already includes the
[img] tag, so you won't need to add it.
Regardless of the option you chose, you should arrive at the following conclusion:
[img]https://i.imgur.com/bIRhQJv.jpg[/img]Which, of course, displays as intended: