World Texture as Alpha

Okay, the title probably doesn’t help with what I need at all. Basically, I have a model, and I need it to be reflecting a background image, but I need the actual background to be a solid color or alpha. The problem is, I don’t know any way besides setting a world texture to effectively make an image reflect on something.

https://blenderartists.org/forum/viewtopic.php?t=53449&highlight=envmap

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When I save the env map, it’s a 300x200 image. I tried resizing it but then it won’t load into Blender. Am I doing something wrong?

edit: I kept the same proportions, of course.