It seems as if we are almost there. The original question: "From what field does the Image Extension extract Business Name."
Answer: Any field in the same account labeled business name such as the business name field in the location extension. In as much as extensions can be set up at the account level, the image extension may pull a business name from an account-level extension. However, the image extension will not pull a business name from a separate campaign or ad group, and the image extension will not pull a business name from the Account Name field in the account preferences settings.
Is this what you have been saying?
Separately, perhaps you could submit a suggestion that the image extension have its own Business Name field so this can be set more explicitly.