This is how you add network image:

Go to settings through the dropdown on the upper-right of the forum by hovering on your Forum Name.


Click on the Personal Information Panel.


Click the Network Image Icon.


Enter the address of the image. You can see that it has to be encapsulated by the "" element.

I think you need to level up your account on this forum before you can do the function. As for your level, its still limited.