to implement it you paste the direct link to the image in between the [img][ /img] blocks.
so for example, it would be like [img ] cubes.png [/ img], but without the spaces.
As for critique, I'd say perspective is off, like it's tilting towards the camera. A combination of factors is causing this, from the lack of detail at the base compared to the top to the castle's crest being tilted, as well as the lack of a discernable "base", what with it being hidden behind the grass.
Also kind of hard to see the guy against those hills, but that may simply be my color blindness acting up.