Compositing a composited image with a render

I have taken two images (deck plating and a flame wall) and composited them to create a background and now I am trying to composite that with a rendered image. The problem I am having comes when I composite the two together, the background/world for my render is effecting the image that I am trying to composite it with. I have been trying to use an Alpha Over Node but this ends up factoring the images together such that the background is effected and the rendered image becomes semi-transparent. What I want to accomplish is to have the deck plate/flame composite in the background with the text and helm in the forground. Any help with this would be greatly appreciated. I am working on getting a file for it uploaded.

A screen shot or blend file as an example would help your description. Sounds like your keyed foreground image may not have the alpha channel that you want.

If any of your nodes have a Clamp option, check the box. All colors fall within a range from 0.0 to 1.0, but sometimes when you use Add or Subtract or some other nodes, the value can exceed 1.0 or fall below 0. When this happens you can get some weird results.

Steve S

Sorry for not getting back to you guys, I was offline for a while. I did find a way of solving my problem with a mask and green screen effect though. Thanks for the comments.

Cool. Goto the first post and choose edit advanced, then change the title to solved. Also try and update the thread with some detail about what the problem was so that other people can gain from your experience.