Shadows are pretty hard to make, since Chroma Key must have a background which would have to have the shadow, since the foreground is being put on top. Maybe if I add the shadow after, but I am really no good at shadows.
As for the black line, It is either that or the picture becomes slightly transparent. (It already is a little if you look closely)
Ever tried making something like this? Take the glest characters, use an image editing software to give it a bright green background, then use a chroma key software (I don't know any, I used a VIDEO editing software called Sony Vegas Movie Studio 8.0, and it's not free) to slap it onto a background, which in my case could be a video clip onto another video clip.
Works great, but mine adds some transparency to it, and you'd need a $1000+ software to get it non transparent.