Ok, well here is how to do it...
1st, you want to click reply...
Have your image saved to your hard drive or desktop
then click on the highlighted icon

then this box should pop up

Click on "Browse" to look for your desired photo on your hard drive.
Then make sure the Width is the "forums" one.
Then click "Host It"
Once it has loaded, you should have a box looking like this.

Click on "Copy" on the middle one, then click on text area and click paste.