can you blend a transparent planes in a scene with heavy mist ?

I"m new to blender and i’ve been experimenting quite a bit with it. currently I am trying to create a scene that has very heavy mist/fog in it and part of that scene contains characters on transparent image planes. the problem is that whenever I render this, I realize that the shape around the character within the plane doesn’t blend in with the background ( here’s what i’m talking about: is there anything I can possibly do to solve this or any solution at all. I am currently using blender 2.69 in the internal rendering engine. thank you