There's two problems: wasting paper and having to manually enter the receipt into an expenses system. You don't have to solve both problems at once.

yes, but i was wondering about the 1st one, which would have a large impact on the rain forests :)

As for #2, i'd say there are so many different formats of receipts that it could prove unfeasible, although just extracting the receipt values could be done, i guess.

the advantage i see in the business owner signing up, as opposed to a more detached solution, it that the business could be categorized in the "backend" (by industry type and etc), and that information would help automatically tagging the receipts (expense type), for example

Stores tend to put their name on the receipt (or at least the large ones do), which you could cross-reference against a list on the server. Alternatively, if you've used your phone to capture the receipt, you've got probably got geotagging information on the image.