Weird browser plug-in blocking you perhaps? Can you try a different web browser? And, for something that you copy and cannot paste into a post, can you paste it into, say, Notepad (assuming you're using Windows)? That will show that copying is at least working. Likewise, does copying something from Notepad into a post work?
"If you can provide an example, we can try and work through it"
I had to type the above message because I couldn't highlight and right click, then copy, then paste and I could not highlight then ctrl + C or ctrl + V.
You can do so in the "quick reply" box. Another example would be if I wanted to share a link, I couldn't copy it from the address bar and paste into the body of the paragraph, I would have to type it out.
It could be my browser at work, we have a lot of restrictions, but it works on all my other forums. I did test Copy/paste in microsoft word to check. The copy/paste works on this forum if I do it in the "quick reply box". I'll try it when I get home.
If possible set pictures to open onto a new window and not the same. This way the main page stays on when closing the picture screen.
Unfortunately, nothing within or about this forum to force that to happen automatically as of yet. You can try right-clicking (if your computer supports it) and choosing to "Open Link in New Tab" or, as another member mentioned, you can try Ctrl-click, which seems faster than right-clicking.