From the main page: click Post A New Topic (Top left corner)
Next: Click Host an Image (6th square from the right) Click on it
After you click this box your box heading will say "upload your image" From here you will browse for your photo that you are wanting to upload. After you have chosen your photo in the same"upload your image" box resize your image from the dropdown menu. I usually resize mine to 640px. Now you will click "host it" This may take it a second.
A new box will pop up with three options: Thumbnail, image, or image url. Copy and paste the middle link.
After you click copy go back and click the 6th square that you clicked on in step one. This should make your box disappear. Now in the big white box right click and past your image. Then press send.
Hopes this helps