I was using Imgur upload there and paste here
Or if you are using steam
1. F12 to take the screen shot.
2. Shift + Tab opens the steam overlay while the game is still running. Click on screenshots and upload the ones you want.
3. Either close or Alt+Tab from the game and open the steam client.
4, Click on 'your name' >> content >> screenshots.
5. Left click on the shot you want to post, then left click on it again. It should spawn a smaller window with your screenshot in it.
6. Right-click on the shot and choose "Copy image URL".
7. Ctrl+V the link in the reply box on CustomsForge. It will auto-replace your link with an image.
(Copy and pasted) ^^^