The easiest way is to simply upload photos from your computer directly to the E9 Forum. When you are creating a message, there is a section below the text box headed "Additional Options". Within that, there is a box labeled "Attach Files". Click that, navigate to the picture you want displayed, select it, and follow the directions.
Only downside is that the resulting photo is displayed kind of small. But other users can expand it by clicking on it. Here's an example: