Albert
When you post on a forum the html is different from the way you have used on the other board.
From your Fotki account follow these steps, click on the thumbnail, now while viewing the mid-size image click on the box that says "Share photo", that will add some code options under the image but you want to click on "more sharing options", use the html in the "Code for Forums" box and you're good to go.
One advantage of doing it this way is that your pics will also be "clickable" to take visitors to your album!
Let me know if you have any questions!
Here's an example, click on it and you'll see what I mean...