This probably wouldn't be a bad topic to sticky since it seems a few others have also had the same question/problem.
Easiest way is:
1. Get the FEN notation of the position you want to copy. In chessbase you can do this by going to edit->copy position. In ICC you can get it by typing: "/fen" and then copying the numbers/letters it gives.
2. Go to http://www.chessvideos.tv/chess-diagram-generator.php
3. Paste the FEN code into the appropriate box on the site. Click generate.
4. Now make sure you have the view facing from the proper side and the correct color set to move. Click generate diagram.
5. Copy the code from the box labeled "Just the image:" and paste it into a post.