I have poked around some and it appears that the only way to get this truly fixed is to create a new background format that is similar to walls. That is, have each background viewpoint available in separate images and use transparency. Transparency is the key in this. Backgrounds don't use it, and it is the only way to draw non-rectangular images.
DC supports multiple formats for wall images, but not currently for backgrounds. The format support allows the default images to be loaded plus any future defined format, and can display all formats at the same time. I don't think it is hard to convert backgrounds to use multiple formats, but there are some details yet to be worked out in drawing the different parts.
If it works, the results should be ok from any direction and distance, but some new backgrounds will need to be created. I'll create one or two samples that demonstrate how it works and include them in the install.
I'm not sure how long this will take, but I'll try to get started on it this weekend.
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CocoaSpud
Dungeon Craft Development Team
http://uaf.sourceforge.net