Hacking Backgrounds on Mac
Big Business Client keeps a folder of textures for Backgrounds. Do not add your own.
You could copy files into Big Business 14 Client's subfolder in Contents, Resources, BBIcons, texture, by first right clicking on Client and clicking Show Package Contents.
However, if your image it too small to cover the screen or too large to load quickly or any number of other possible problems it could go badly and you should play it safe.
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